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	$233.67	6.251%	$248.2767	$248.28	$248.30	$248.30
Purchase #2	$40.87	11.251%	$45.4683	$45.47	$45.45	$45.50
Purchase #3	$166.80	13.501%	$189.3197	$189.32	$189.30	$189.30
Purchase #4	$204.43	9.551%	$223.9551	$223.96	$223.95	$224.00
Purchase #5	$70.39	10.859%	$78.0337	$78.03	$78.05	$78.00
Purchase #6	$139.55	11.472%	$155.5592	$155.56	$155.55	$155.60
Purchase #7	$45.36	8.378%	$49.1603	$49.16	$49.15	$49.20
7 purchase totals =	$901.07		$989.7730	$989.78	$989.75	$989.90