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	$139.60	12.135%	$156.5405	$156.54	$156.55	$156.50
Purchase #2	$52.37	12.826%	$59.087	$59.09	$59.10	$59.10
Purchase #3	$6.85	10.846%	$7.593	$7.59	$7.60	$7.60
Purchase #4	$53.74	7.134%	$57.5738	$57.57	$57.55	$57.60
Purchase #5	$19.97	6.790%	$21.326	$21.33	$21.35	$21.30
Purchase #6	$116.51	12.140%	$130.6543	$130.65	$130.65	$130.70
Purchase #7	$48.42	13.225%	$54.8235	$54.82	$54.80	$54.80
7 purchase totals =	$437.46		$487.5981	$487.59	$487.60	$487.60