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	$54.32	12.873%	$61.3126	$61.31	$61.30	$61.30
Purchase #2	$213.51	7.616%	$229.7709	$229.77	$229.75	$229.80
Purchase #3	$17.95	10.593%	$19.8514	$19.85	$19.85	$19.90
Purchase #4	$153.49	12.850%	$173.2135	$173.21	$173.20	$173.20
Purchase #5	$85.51	4.567%	$89.4152	$89.42	$89.40	$89.40
Purchase #6	$35.91	3.413%	$37.1356	$37.14	$37.15	$37.10
Purchase #7	$137.67	11.184%	$153.067	$153.07	$153.05	$153.10
7 purchase totals =	$698.36		$763.7662	$763.77	$763.70	$763.80