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	$176.34	7.645%	$189.8212	$189.82	$189.80	$189.80
Purchase #2	$123.41	8.669%	$134.1084	$134.11	$134.10	$134.10
Purchase #3	$67.81	13.469%	$76.9433	$76.94	$76.95	$76.90
Purchase #4	$87.46	4.716%	$91.5846	$91.58	$91.60	$91.60
Purchase #5	$84.78	12.231%	$95.1494	$95.15	$95.15	$95.10
Purchase #6	$82.50	10.189%	$90.9059	$90.91	$90.90	$90.90
Purchase #7	$56.74	9.134%	$61.9226	$61.92	$61.90	$61.90
7 purchase totals =	$679.04		$740.4354	$740.43	$740.40	$740.30