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	$82.65	12.418%	$92.9135	$92.91	$92.90	$92.90
Purchase #2	$163.44	13.569%	$185.6172	$185.62	$185.60	$185.60
Purchase #3	$152.94	9.673%	$167.7339	$167.73	$167.75	$167.70
Purchase #4	$132.35	6.333%	$140.7317	$140.73	$140.75	$140.70
Purchase #5	$124.82	13.335%	$141.4647	$141.46	$141.45	$141.50
Purchase #6	$95.70	13.456%	$108.5774	$108.58	$108.60	$108.60
Purchase #7	$54.75	11.682%	$61.1459	$61.15	$61.15	$61.10
7 purchase totals =	$806.65		$898.1843	$898.18	$898.20	$898.10