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	$133.57	3.161%	$137.7921	$137.79	$137.80	$137.80
Purchase #2	$229.71	5.846%	$243.1388	$243.14	$243.15	$243.10
Purchase #3	$155.25	4.152%	$161.696	$161.70	$161.70	$161.70
Purchase #4	$63.69	13.208%	$72.1022	$72.10	$72.10	$72.10
Purchase #5	$131.65	11.607%	$146.9306	$146.93	$146.95	$146.90
Purchase #6	$171.81	4.422%	$179.4074	$179.41	$179.40	$179.40
Purchase #7	$191.95	11.456%	$213.9398	$213.94	$213.95	$213.90
7 purchase totals =	$1,077.63		$1,155.0069	$1,155.01	$1,155.05	$1,154.90