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	$74.98	10.307%	$82.7082	$82.71	$82.70	$82.70
Purchase #2	$39.77	7.102%	$42.5945	$42.59	$42.60	$42.60
Purchase #3	$169.76	5.163%	$178.5247	$178.52	$178.50	$178.50
Purchase #4	$136.57	8.295%	$147.8985	$147.90	$147.90	$147.90
Purchase #5	$115.89	8.615%	$125.8739	$125.87	$125.85	$125.90
Purchase #6	$136.72	7.456%	$146.9138	$146.91	$146.90	$146.90
Purchase #7	$60.85	13.429%	$69.0215	$69.02	$69.00	$69.00
7 purchase totals =	$734.54		$793.5351	$793.52	$793.45	$793.50