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	$58.78	9.157%	$64.1625	$64.16	$64.15	$64.20
Purchase #2	$114.65	3.430%	$118.5825	$118.58	$118.60	$118.60
Purchase #3	$130.59	8.315%	$141.4486	$141.45	$141.45	$141.40
Purchase #4	$230.41	8.873%	$250.8543	$250.85	$250.85	$250.90
Purchase #5	$90.58	3.815%	$94.0356	$94.04	$94.05	$94.00
Purchase #6	$64.45	11.486%	$71.8527	$71.85	$71.85	$71.90
Purchase #7	$200.61	8.375%	$217.4111	$217.41	$217.40	$217.40
7 purchase totals =	$890.07		$958.3473	$958.34	$958.35	$958.40