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	$20.37	8.166%	$22.0334	$22.03	$22.05	$22.00
Purchase #2	$178.89	3.541%	$185.2245	$185.22	$185.20	$185.20
Purchase #3	$180.36	10.773%	$199.7902	$199.79	$199.80	$199.80
Purchase #4	$124.31	5.524%	$131.1769	$131.18	$131.20	$131.20
Purchase #5	$73.39	13.605%	$83.3747	$83.37	$83.35	$83.40
Purchase #6	$165.92	11.206%	$184.513	$184.51	$184.50	$184.50
Purchase #7	$166.66	5.318%	$175.523	$175.52	$175.50	$175.50
7 purchase totals =	$909.90		$981.6357	$981.62	$981.60	$981.60