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	$108.88	13.420%	$123.4917	$123.49	$123.50	$123.50
Purchase #2	$83.72	8.804%	$91.0907	$91.09	$91.10	$91.10
Purchase #3	$123.78	9.650%	$135.7248	$135.72	$135.70	$135.70
Purchase #4	$65.93	8.310%	$71.4088	$71.41	$71.40	$71.40
Purchase #5	$152.51	8.478%	$165.4398	$165.44	$165.45	$165.40
Purchase #6	$59.77	12.375%	$67.1665	$67.17	$67.15	$67.20
Purchase #7	$123.95	13.308%	$140.4453	$140.45	$140.45	$140.40
7 purchase totals =	$718.54		$794.7676	$794.77	$794.75	$794.70