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	$156.75	10.690%	$173.5066	$173.51	$173.50	$173.50
Purchase #2	$205.82	8.117%	$222.5264	$222.53	$222.55	$222.50
Purchase #3	$134.32	13.832%	$152.8991	$152.90	$152.90	$152.90
Purchase #4	$143.68	5.424%	$151.4732	$151.47	$151.45	$151.50
Purchase #5	$75.65	4.802%	$79.2827	$79.28	$79.30	$79.30
Purchase #6	$223.34	9.688%	$244.9772	$244.98	$245.00	$245.00
Purchase #7	$215.49	11.505%	$240.2821	$240.28	$240.30	$240.30
7 purchase totals =	$1,155.05		$1,264.9473	$1,264.95	$1,265.00	$1,265.00