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	$105.58	6.850%	$112.8122	$112.81	$112.80	$112.80
Purchase #2	$240.77	12.501%	$270.8687	$270.87	$270.85	$270.90
Purchase #3	$63.63	11.463%	$70.9239	$70.92	$70.90	$70.90
Purchase #4	$151.29	12.512%	$170.2194	$170.22	$170.20	$170.20
Purchase #5	$250.83	9.733%	$275.2433	$275.24	$275.25	$275.20
Purchase #6	$100.34	5.117%	$105.4744	$105.47	$105.45	$105.50
Purchase #7	$233.57	13.168%	$264.3265	$264.33	$264.35	$264.30
7 purchase totals =	$1,146.01		$1,269.8684	$1,269.86	$1,269.80	$1,269.80