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	$33.84	10.267%	$37.3144	$37.31	$37.30	$37.30
Purchase #2	$206.31	8.460%	$223.7638	$223.76	$223.75	$223.80
Purchase #3	$168.63	8.312%	$182.6465	$182.65	$182.65	$182.60
Purchase #4	$151.77	12.189%	$170.2692	$170.27	$170.25	$170.30
Purchase #5	$110.32	5.243%	$116.1041	$116.10	$116.10	$116.10
Purchase #6	$17.68	3.699%	$18.334	$18.33	$18.35	$18.30
Purchase #7	$156.33	10.603%	$172.9057	$172.91	$172.90	$172.90
7 purchase totals =	$844.88		$921.3377	$921.33	$921.30	$921.30