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	$48.64	5.574%	$51.3512	$51.35	$51.35	$51.40
Purchase #2	$11.86	3.115%	$12.2294	$12.23	$12.25	$12.20
Purchase #3	$71.89	13.696%	$81.7361	$81.74	$81.75	$81.70
Purchase #4	$60.56	13.197%	$68.5521	$68.55	$68.55	$68.60
Purchase #5	$115.33	10.559%	$127.5077	$127.51	$127.50	$127.50
Purchase #6	$59.67	13.267%	$67.5864	$67.59	$67.60	$67.60
Purchase #7	$166.70	13.848%	$189.7846	$189.78	$189.80	$189.80
7 purchase totals =	$534.65		$598.7475	$598.75	$598.80	$598.80