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	$33.48	10.299%	$36.9281	$36.93	$36.95	$36.90
Purchase #2	$61.89	13.799%	$70.4302	$70.43	$70.45	$70.40
Purchase #3	$220.73	6.576%	$235.2452	$235.25	$235.25	$235.20
Purchase #4	$242.78	11.587%	$270.9109	$270.91	$270.90	$270.90
Purchase #5	$65.96	9.105%	$71.9657	$71.97	$71.95	$72.00
Purchase #6	$94.45	6.726%	$100.8027	$100.80	$100.80	$100.80
Purchase #7	$179.74	11.496%	$200.4029	$200.40	$200.40	$200.40
7 purchase totals =	$899.03		$986.6857	$986.69	$986.70	$986.60