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	$159.66	12.823%	$180.1332	$180.13	$180.15	$180.10
Purchase #2	$49.85	8.227%	$53.9512	$53.95	$53.95	$54.00
Purchase #3	$36.80	6.604%	$39.2303	$39.23	$39.25	$39.20
Purchase #4	$184.52	6.515%	$196.5415	$196.54	$196.55	$196.50
Purchase #5	$234.88	12.763%	$264.8577	$264.86	$264.85	$264.90
Purchase #6	$238.45	4.786%	$249.8622	$249.86	$249.85	$249.90
Purchase #7	$128.80	7.740%	$138.7691	$138.77	$138.75	$138.80
7 purchase totals =	$1,032.96		$1,123.3452	$1,123.34	$1,123.35	$1,123.40