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	$152.78	12.513%	$171.8974	$171.90	$171.90	$171.90
Purchase #2	$172.69	6.380%	$183.7076	$183.71	$183.70	$183.70
Purchase #3	$138.33	8.731%	$150.4076	$150.41	$150.40	$150.40
Purchase #4	$12.68	5.508%	$13.3784	$13.38	$13.40	$13.40
Purchase #5	$171.38	10.314%	$189.0561	$189.06	$189.05	$189.10
Purchase #6	$159.84	4.743%	$167.4212	$167.42	$167.40	$167.40
Purchase #7	$83.81	7.549%	$90.1368	$90.14	$90.15	$90.10
7 purchase totals =	$891.51		$966.0051	$966.02	$966.00	$966.00