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	$40.75	12.227%	$45.7325	$45.73	$45.75	$45.70
Purchase #2	$221.35	3.849%	$229.8698	$229.87	$229.85	$229.90
Purchase #3	$58.87	10.128%	$64.8324	$64.83	$64.85	$64.80
Purchase #4	$169.49	11.209%	$188.4881	$188.49	$188.50	$188.50
Purchase #5	$87.86	13.660%	$99.8617	$99.86	$99.85	$99.90
Purchase #6	$6.72	3.470%	$6.9532	$6.95	$6.95	$7.00
Purchase #7	$9.91	9.306%	$10.8322	$10.83	$10.85	$10.80
7 purchase totals =	$594.95		$646.5699	$646.56	$646.60	$646.60