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	$109.34	6.203%	$116.1224	$116.12	$116.10	$116.10
Purchase #2	$51.63	11.439%	$57.536	$57.54	$57.55	$57.50
Purchase #3	$223.84	4.318%	$233.5054	$233.51	$233.50	$233.50
Purchase #4	$34.64	7.144%	$37.1147	$37.11	$37.10	$37.10
Purchase #5	$64.54	8.671%	$70.1363	$70.14	$70.15	$70.10
Purchase #6	$157.89	7.419%	$169.6039	$169.60	$169.60	$169.60
Purchase #7	$135.92	12.434%	$152.8203	$152.82	$152.80	$152.80
7 purchase totals =	$777.80		$836.8390	$836.84	$836.80	$836.70