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	$57.62	13.114%	$65.1763	$65.18	$65.20	$65.20
Purchase #2	$24.80	12.604%	$27.9258	$27.93	$27.95	$27.90
Purchase #3	$36.91	6.385%	$39.2667	$39.27	$39.25	$39.30
Purchase #4	$219.95	12.551%	$247.5559	$247.56	$247.55	$247.60
Purchase #5	$127.75	5.553%	$134.844	$134.84	$134.85	$134.80
Purchase #6	$53.80	10.546%	$59.4737	$59.47	$59.45	$59.50
Purchase #7	$89.95	10.788%	$99.6538	$99.65	$99.65	$99.70
7 purchase totals =	$610.78		$673.8962	$673.90	$673.90	$674.00