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	$242.31	13.704%	$275.5162	$275.52	$275.50	$275.50
Purchase #2	$223.26	5.103%	$234.653	$234.65	$234.65	$234.70
Purchase #3	$137.74	9.466%	$150.7785	$150.78	$150.80	$150.80
Purchase #4	$28.69	13.816%	$32.6538	$32.65	$32.65	$32.70
Purchase #5	$160.90	3.310%	$166.2258	$166.23	$166.25	$166.20
Purchase #6	$224.92	13.468%	$255.2122	$255.21	$255.20	$255.20
Purchase #7	$6.77	8.650%	$7.3556	$7.36	$7.35	$7.40
7 purchase totals =	$1,024.59		$1,122.3951	$1,122.40	$1,122.40	$1,122.50