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	$30.75	3.771%	$31.9096	$31.91	$31.90	$31.90
Purchase #2	$92.42	8.338%	$100.126	$100.13	$100.15	$100.10
Purchase #3	$40.77	10.433%	$45.0235	$45.02	$45.00	$45.00
Purchase #4	$177.65	13.633%	$201.869	$201.87	$201.85	$201.90
Purchase #5	$30.78	8.172%	$33.2953	$33.30	$33.30	$33.30
Purchase #6	$148.82	5.318%	$156.7342	$156.73	$156.75	$156.70
Purchase #7	$87.71	13.311%	$99.3851	$99.39	$99.40	$99.40
7 purchase totals =	$608.90		$668.3427	$668.35	$668.35	$668.30