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	$29.85	12.819%	$33.6765	$33.68	$33.70	$33.70
Purchase #2	$29.95	9.807%	$32.8872	$32.89	$32.90	$32.90
Purchase #3	$68.71	6.527%	$73.1947	$73.19	$73.20	$73.20
Purchase #4	$146.96	9.131%	$160.3789	$160.38	$160.40	$160.40
Purchase #5	$61.72	8.151%	$66.7508	$66.75	$66.75	$66.80
Purchase #6	$20.80	3.295%	$21.4854	$21.49	$21.50	$21.50
Purchase #7	$244.47	13.644%	$277.8255	$277.83	$277.85	$277.80
7 purchase totals =	$602.46		$666.1990	$666.21	$666.30	$666.30