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	$122.30	12.768%	$137.9153	$137.92	$137.90	$137.90
Purchase #2	$81.94	8.804%	$89.154	$89.15	$89.15	$89.20
Purchase #3	$99.79	11.699%	$111.4644	$111.46	$111.45	$111.50
Purchase #4	$173.61	13.394%	$196.8633	$196.86	$196.85	$196.90
Purchase #5	$28.42	3.211%	$29.3326	$29.33	$29.35	$29.30
Purchase #6	$207.57	10.717%	$229.8153	$229.82	$229.80	$229.80
Purchase #7	$155.55	3.483%	$160.9678	$160.97	$160.95	$161.00
7 purchase totals =	$869.18		$955.5127	$955.51	$955.45	$955.60