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	$95.32	7.130%	$102.1163	$102.12	$102.10	$102.10
Purchase #2	$158.81	8.733%	$172.6789	$172.68	$172.70	$172.70
Purchase #3	$39.80	5.261%	$41.8939	$41.89	$41.90	$41.90
Purchase #4	$73.59	10.518%	$81.3302	$81.33	$81.35	$81.30
Purchase #5	$65.36	7.841%	$70.4849	$70.48	$70.50	$70.50
Purchase #6	$42.96	6.318%	$45.6742	$45.67	$45.65	$45.70
Purchase #7	$99.67	7.204%	$106.8502	$106.85	$106.85	$106.90
7 purchase totals =	$575.51		$621.0286	$621.02	$621.05	$621.10