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	$173.32	9.707%	$190.1442	$190.14	$190.15	$190.10
Purchase #2	$43.74	8.552%	$47.4806	$47.48	$47.50	$47.50
Purchase #3	$107.77	10.690%	$119.2906	$119.29	$119.30	$119.30
Purchase #4	$38.57	10.181%	$42.4968	$42.50	$42.50	$42.50
Purchase #5	$191.82	6.718%	$204.7065	$204.71	$204.70	$204.70
Purchase #6	$138.77	12.332%	$155.8831	$155.88	$155.90	$155.90
Purchase #7	$165.25	3.846%	$171.6055	$171.61	$171.60	$171.60
7 purchase totals =	$859.24		$931.6073	$931.61	$931.65	$931.60