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	$198.29	7.224%	$212.6145	$212.61	$212.60	$212.60
Purchase #2	$53.51	11.404%	$59.6123	$59.61	$59.60	$59.60
Purchase #3	$250.59	13.221%	$283.7205	$283.72	$283.70	$283.70
Purchase #4	$128.46	3.866%	$133.4263	$133.43	$133.45	$133.40
Purchase #5	$100.33	9.434%	$109.7951	$109.80	$109.80	$109.80
Purchase #6	$197.83	13.635%	$224.8041	$224.80	$224.80	$224.80
Purchase #7	$132.88	6.841%	$141.9703	$141.97	$141.95	$142.00
7 purchase totals =	$1,061.89		$1,165.9431	$1,165.94	$1,165.90	$1,165.90