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	$37.61	6.833%	$40.1799	$40.18	$40.20	$40.20
Purchase #2	$132.44	6.828%	$141.483	$141.48	$141.50	$141.50
Purchase #3	$240.55	9.145%	$262.5483	$262.55	$262.55	$262.50
Purchase #4	$72.53	12.570%	$81.647	$81.65	$81.65	$81.60
Purchase #5	$96.41	12.773%	$108.7244	$108.72	$108.70	$108.70
Purchase #6	$6.35	13.307%	$7.195	$7.20	$7.20	$7.20
Purchase #7	$83.67	9.321%	$91.4689	$91.47	$91.45	$91.50
7 purchase totals =	$669.56		$733.2465	$733.25	$733.25	$733.20