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	$104.32	12.738%	$117.6083	$117.61	$117.60	$117.60
Purchase #2	$155.63	7.674%	$167.573	$167.57	$167.55	$167.60
Purchase #3	$37.55	12.134%	$42.1063	$42.11	$42.10	$42.10
Purchase #4	$193.50	10.830%	$214.4561	$214.46	$214.45	$214.50
Purchase #5	$163.89	9.422%	$179.3317	$179.33	$179.35	$179.30
Purchase #6	$132.81	3.134%	$136.9723	$136.97	$136.95	$137.00
Purchase #7	$103.68	9.488%	$113.5172	$113.52	$113.50	$113.50
7 purchase totals =	$891.38		$971.5649	$971.57	$971.50	$971.60