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	$39.84	7.221%	$42.7168	$42.72	$42.70	$42.70
Purchase #2	$24.50	7.860%	$26.4257	$26.43	$26.45	$26.40
Purchase #3	$152.71	12.231%	$171.388	$171.39	$171.40	$171.40
Purchase #4	$197.72	4.639%	$206.8922	$206.89	$206.90	$206.90
Purchase #5	$199.78	6.861%	$213.4869	$213.49	$213.50	$213.50
Purchase #6	$47.76	7.680%	$51.428	$51.43	$51.45	$51.40
Purchase #7	$127.51	9.183%	$139.2192	$139.22	$139.20	$139.20
7 purchase totals =	$789.82		$851.5568	$851.57	$851.60	$851.50