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	$79.41	12.435%	$89.2846	$89.28	$89.30	$89.30
Purchase #2	$42.28	3.593%	$43.7991	$43.80	$43.80	$43.80
Purchase #3	$192.49	8.659%	$209.1577	$209.16	$209.15	$209.20
Purchase #4	$124.87	4.420%	$130.3893	$130.39	$130.40	$130.40
Purchase #5	$33.83	12.604%	$38.0939	$38.09	$38.10	$38.10
Purchase #6	$166.96	5.317%	$175.8373	$175.84	$175.85	$175.80
Purchase #7	$159.79	6.349%	$169.9351	$169.94	$169.95	$169.90
7 purchase totals =	$799.63		$856.4970	$856.50	$856.55	$856.50