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	$89.40	12.390%	$100.4767	$100.48	$100.50	$100.50
Purchase #2	$146.82	10.454%	$162.1686	$162.17	$162.15	$162.20
Purchase #3	$133.30	10.806%	$147.7044	$147.70	$147.70	$147.70
Purchase #4	$223.87	9.630%	$245.4287	$245.43	$245.45	$245.40
Purchase #5	$194.80	13.587%	$221.2675	$221.27	$221.25	$221.30
Purchase #6	$195.79	6.548%	$208.6103	$208.61	$208.60	$208.60
Purchase #7	$6.84	4.233%	$7.1295	$7.13	$7.15	$7.10
7 purchase totals =	$990.82		$1,092.7857	$1,092.79	$1,092.80	$1,092.80