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	$136.69	3.266%	$141.1543	$141.15	$141.15	$141.20
Purchase #2	$42.79	8.134%	$46.2705	$46.27	$46.25	$46.30
Purchase #3	$59.77	4.500%	$62.4597	$62.46	$62.45	$62.50
Purchase #4	$128.50	6.668%	$137.0684	$137.07	$137.05	$137.10
Purchase #5	$24.94	6.563%	$26.5768	$26.58	$26.60	$26.60
Purchase #6	$87.37	3.734%	$90.6324	$90.63	$90.65	$90.60
Purchase #7	$156.51	5.761%	$165.5265	$165.53	$165.55	$165.50
7 purchase totals =	$636.57		$669.6886	$669.69	$669.70	$669.80