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	$25.55	11.263%	$28.4277	$28.43	$28.45	$28.40
Purchase #2	$111.57	5.534%	$117.7443	$117.74	$117.75	$117.70
Purchase #3	$91.61	5.546%	$96.6907	$96.69	$96.70	$96.70
Purchase #4	$173.88	10.112%	$191.4627	$191.46	$191.45	$191.50
Purchase #5	$6.65	10.575%	$7.3532	$7.35	$7.35	$7.40
Purchase #6	$153.77	4.671%	$160.9526	$160.95	$160.95	$161.00
Purchase #7	$212.95	4.478%	$222.4859	$222.49	$222.50	$222.50
7 purchase totals =	$775.98		$825.1171	$825.11	$825.15	$825.20