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	$63.38	13.417%	$71.8837	$71.88	$71.90	$71.90
Purchase #2	$105.97	13.792%	$120.5854	$120.59	$120.60	$120.60
Purchase #3	$25.43	12.194%	$28.5309	$28.53	$28.55	$28.50
Purchase #4	$7.89	7.642%	$8.493	$8.49	$8.50	$8.50
Purchase #5	$216.25	8.281%	$234.1577	$234.16	$234.15	$234.20
Purchase #6	$79.84	13.537%	$90.6479	$90.65	$90.65	$90.60
Purchase #7	$221.98	8.399%	$240.6241	$240.62	$240.60	$240.60
7 purchase totals =	$720.74		$794.9227	$794.92	$794.95	$794.90