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	$224.45	7.800%	$241.9571	$241.96	$241.95	$242.00
Purchase #2	$42.36	13.587%	$48.1155	$48.12	$48.10	$48.10
Purchase #3	$59.68	13.410%	$67.6831	$67.68	$67.70	$67.70
Purchase #4	$105.69	5.685%	$111.6985	$111.70	$111.70	$111.70
Purchase #5	$106.54	5.263%	$112.1472	$112.15	$112.15	$112.10
Purchase #6	$115.70	3.860%	$120.166	$120.17	$120.15	$120.20
Purchase #7	$90.73	9.240%	$99.1135	$99.11	$99.10	$99.10
7 purchase totals =	$745.15		$800.8809	$800.89	$800.85	$800.90