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	$18.84	13.607%	$21.4036	$21.40	$21.40	$21.40
Purchase #2	$53.89	11.467%	$60.0696	$60.07	$60.05	$60.10
Purchase #3	$56.87	7.442%	$61.1023	$61.10	$61.10	$61.10
Purchase #4	$149.51	3.312%	$154.4618	$154.46	$154.45	$154.50
Purchase #5	$65.93	8.729%	$71.685	$71.69	$71.70	$71.70
Purchase #6	$22.62	11.628%	$25.2503	$25.25	$25.25	$25.30
Purchase #7	$38.35	13.582%	$43.5587	$43.56	$43.55	$43.60
7 purchase totals =	$406.01		$437.5313	$437.53	$437.50	$437.70