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	$98.41	11.136%	$109.3689	$109.37	$109.35	$109.40
Purchase #2	$132.46	4.794%	$138.8101	$138.81	$138.80	$138.80
Purchase #3	$180.90	5.461%	$190.7789	$190.78	$190.80	$190.80
Purchase #4	$250.55	4.237%	$261.1658	$261.17	$261.15	$261.20
Purchase #5	$151.61	9.297%	$165.7052	$165.71	$165.70	$165.70
Purchase #6	$182.85	13.148%	$206.8911	$206.89	$206.90	$206.90
Purchase #7	$89.29	3.114%	$92.0705	$92.07	$92.05	$92.10
7 purchase totals =	$1,086.07		$1,164.7905	$1,164.80	$1,164.75	$1,164.90