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	$172.72	4.317%	$180.1763	$180.18	$180.20	$180.20
Purchase #2	$20.86	4.629%	$21.8256	$21.83	$21.85	$21.80
Purchase #3	$143.42	12.494%	$161.3389	$161.34	$161.35	$161.30
Purchase #4	$183.97	12.461%	$206.8945	$206.89	$206.90	$206.90
Purchase #5	$42.63	7.512%	$45.8324	$45.83	$45.85	$45.80
Purchase #6	$94.36	11.827%	$105.52	$105.52	$105.50	$105.50
Purchase #7	$245.67	12.198%	$275.6368	$275.64	$275.65	$275.60
7 purchase totals =	$903.63		$997.2245	$997.23	$997.30	$997.10