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	$153.33	12.502%	$172.4993	$172.50	$172.50	$172.50
Purchase #2	$138.37	6.179%	$146.9199	$146.92	$146.90	$146.90
Purchase #3	$40.92	3.443%	$42.3289	$42.33	$42.35	$42.30
Purchase #4	$176.69	9.749%	$193.9155	$193.92	$193.90	$193.90
Purchase #5	$175.92	7.679%	$189.4289	$189.43	$189.45	$189.40
Purchase #6	$141.61	8.600%	$153.7885	$153.79	$153.80	$153.80
Purchase #7	$136.51	3.137%	$140.7923	$140.79	$140.80	$140.80
7 purchase totals =	$963.35		$1,039.6733	$1,039.68	$1,039.70	$1,039.60