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	$152.54	12.596%	$171.7539	$171.75	$171.75	$171.80
Purchase #2	$123.44	7.579%	$132.7955	$132.80	$132.80	$132.80
Purchase #3	$126.52	12.624%	$142.4919	$142.49	$142.50	$142.50
Purchase #4	$11.98	7.457%	$12.8733	$12.87	$12.85	$12.90
Purchase #5	$25.48	6.518%	$27.1408	$27.14	$27.15	$27.10
Purchase #6	$62.35	5.517%	$65.7898	$65.79	$65.80	$65.80
Purchase #7	$215.85	12.715%	$243.2953	$243.30	$243.30	$243.30
7 purchase totals =	$718.16		$796.1405	$796.14	$796.15	$796.20