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	$139.62	11.569%	$155.7726	$155.77	$155.75	$155.80
Purchase #2	$16.29	12.740%	$18.3653	$18.37	$18.35	$18.40
Purchase #3	$217.33	10.564%	$240.2887	$240.29	$240.30	$240.30
Purchase #4	$144.82	7.592%	$155.8147	$155.81	$155.80	$155.80
Purchase #5	$85.92	5.758%	$90.8673	$90.87	$90.85	$90.90
Purchase #6	$27.54	3.278%	$28.4428	$28.44	$28.45	$28.40
Purchase #7	$190.30	6.863%	$203.3603	$203.36	$203.35	$203.40
7 purchase totals =	$821.82		$892.9117	$892.91	$892.85	$893.00