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	$137.27	4.426%	$143.3456	$143.35	$143.35	$143.30
Purchase #2	$242.55	8.833%	$263.9744	$263.97	$263.95	$264.00
Purchase #3	$12.30	4.854%	$12.897	$12.90	$12.90	$12.90
Purchase #4	$246.57	12.865%	$278.2912	$278.29	$278.30	$278.30
Purchase #5	$76.59	11.439%	$85.3511	$85.35	$85.35	$85.40
Purchase #6	$157.39	5.290%	$165.7159	$165.72	$165.70	$165.70
Purchase #7	$18.73	4.449%	$19.5633	$19.56	$19.55	$19.60
7 purchase totals =	$891.40		$969.1385	$969.14	$969.10	$969.20