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	$88.57	12.375%	$99.5305	$99.53	$99.55	$99.50
Purchase #2	$52.70	7.658%	$56.7358	$56.74	$56.75	$56.70
Purchase #3	$85.36	7.530%	$91.7876	$91.79	$91.80	$91.80
Purchase #4	$224.68	13.119%	$254.1558	$254.16	$254.15	$254.20
Purchase #5	$235.55	5.631%	$248.8138	$248.81	$248.80	$248.80
Purchase #6	$176.63	13.635%	$200.7135	$200.71	$200.70	$200.70
Purchase #7	$146.83	7.692%	$158.1242	$158.12	$158.10	$158.10
7 purchase totals =	$1,010.32		$1,109.8612	$1,109.86	$1,109.85	$1,109.80