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	$80.78	11.687%	$90.2208	$90.22	$90.20	$90.20
Purchase #2	$177.90	6.256%	$189.0294	$189.03	$189.05	$189.00
Purchase #3	$33.52	9.853%	$36.8227	$36.82	$36.80	$36.80
Purchase #4	$35.94	13.289%	$40.7161	$40.72	$40.70	$40.70
Purchase #5	$109.35	11.485%	$121.9088	$121.91	$121.90	$121.90
Purchase #6	$56.67	5.589%	$59.8373	$59.84	$59.85	$59.80
Purchase #7	$83.81	4.308%	$87.4205	$87.42	$87.40	$87.40
7 purchase totals =	$577.97		$625.9556	$625.96	$625.90	$625.80