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	$222.31	12.570%	$250.2544	$250.25	$250.25	$250.30
Purchase #2	$179.79	5.319%	$189.353	$189.35	$189.35	$189.40
Purchase #3	$228.72	6.146%	$242.7771	$242.78	$242.80	$242.80
Purchase #4	$245.70	10.173%	$270.6951	$270.70	$270.70	$270.70
Purchase #5	$143.29	5.681%	$151.4303	$151.43	$151.45	$151.40
Purchase #6	$160.49	3.163%	$165.5663	$165.57	$165.55	$165.60
Purchase #7	$95.88	5.146%	$100.814	$100.81	$100.80	$100.80
7 purchase totals =	$1,276.18		$1,370.8902	$1,370.89	$1,370.90	$1,371.00