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	$35.88	4.580%	$37.5233	$37.52	$37.50	$37.50
Purchase #2	$37.92	10.869%	$42.0415	$42.04	$42.05	$42.00
Purchase #3	$7.42	12.844%	$8.373	$8.37	$8.35	$8.40
Purchase #4	$143.78	10.561%	$158.9646	$158.96	$158.95	$159.00
Purchase #5	$44.91	13.336%	$50.8992	$50.90	$50.90	$50.90
Purchase #6	$160.41	7.238%	$172.0205	$172.02	$172.00	$172.00
Purchase #7	$156.46	12.285%	$175.6811	$175.68	$175.70	$175.70
7 purchase totals =	$586.78		$645.5032	$645.49	$645.45	$645.50