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	$235.28	8.430%	$255.1141	$255.11	$255.10	$255.10
Purchase #2	$226.95	12.855%	$256.1244	$256.12	$256.10	$256.10
Purchase #3	$200.53	5.345%	$211.2483	$211.25	$211.25	$211.20
Purchase #4	$149.70	12.798%	$168.8586	$168.86	$168.85	$168.90
Purchase #5	$216.51	5.166%	$227.6949	$227.69	$227.70	$227.70
Purchase #6	$250.61	9.847%	$275.2876	$275.29	$275.30	$275.30
Purchase #7	$234.94	12.470%	$264.237	$264.24	$264.25	$264.20
7 purchase totals =	$1,514.52		$1,658.5649	$1,658.56	$1,658.55	$1,658.50