Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$51.87	13.362%	$58.8009	$58.80	$58.80	$58.80
Purchase #2	$233.87	8.562%	$253.8939	$253.89	$253.90	$253.90
Purchase #3	$129.90	9.365%	$142.0651	$142.07	$142.05	$142.10
Purchase #4	$113.45	12.318%	$127.4248	$127.42	$127.40	$127.40
Purchase #5	$75.30	13.821%	$85.7072	$85.71	$85.70	$85.70
Purchase #6	$175.45	13.151%	$198.5234	$198.52	$198.50	$198.50
Purchase #7	$75.63	12.593%	$85.1541	$85.15	$85.15	$85.20
7 purchase totals =	$855.47		$951.5694	$951.56	$951.50	$951.60