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	$155.54	6.467%	$165.5988	$165.60	$165.60	$165.60
Purchase #2	$247.56	11.503%	$276.0368	$276.04	$276.05	$276.00
Purchase #3	$246.84	12.833%	$278.517	$278.52	$278.50	$278.50
Purchase #4	$80.35	10.231%	$88.5706	$88.57	$88.55	$88.60
Purchase #5	$152.46	6.399%	$162.2159	$162.22	$162.20	$162.20
Purchase #6	$90.33	5.475%	$95.2756	$95.28	$95.30	$95.30
Purchase #7	$56.29	5.781%	$59.5441	$59.54	$59.55	$59.50
7 purchase totals =	$1,029.37		$1,125.7588	$1,125.77	$1,125.75	$1,125.70