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	$91.92	7.809%	$99.098	$99.10	$99.10	$99.10
Purchase #2	$170.52	3.169%	$175.9238	$175.92	$175.90	$175.90
Purchase #3	$151.90	11.222%	$168.9462	$168.95	$168.95	$168.90
Purchase #4	$37.37	8.502%	$40.5472	$40.55	$40.55	$40.50
Purchase #5	$229.34	7.722%	$247.0496	$247.05	$247.05	$247.00
Purchase #6	$52.65	8.636%	$57.1969	$57.20	$57.20	$57.20
Purchase #7	$182.33	3.144%	$188.0625	$188.06	$188.05	$188.10
7 purchase totals =	$916.03		$976.8242	$976.83	$976.80	$976.70