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	$234.91	10.470%	$259.5051	$259.51	$259.50	$259.50
Purchase #2	$36.90	12.512%	$41.5169	$41.52	$41.50	$41.50
Purchase #3	$159.58	9.832%	$175.2699	$175.27	$175.25	$175.30
Purchase #4	$48.96	3.323%	$50.5869	$50.59	$50.60	$50.60
Purchase #5	$43.72	10.758%	$48.4234	$48.42	$48.40	$48.40
Purchase #6	$67.75	5.729%	$71.6314	$71.63	$71.65	$71.60
Purchase #7	$203.34	10.216%	$224.1132	$224.11	$224.10	$224.10
7 purchase totals =	$795.16		$871.0468	$871.05	$871.00	$871.00