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	$203.97	6.105%	$216.4224	$216.42	$216.40	$216.40
Purchase #2	$238.85	11.170%	$265.5295	$265.53	$265.55	$265.50
Purchase #3	$220.74	6.221%	$234.4722	$234.47	$234.45	$234.50
Purchase #4	$141.61	9.567%	$155.1578	$155.16	$155.15	$155.20
Purchase #5	$139.44	11.374%	$155.2999	$155.30	$155.30	$155.30
Purchase #6	$160.33	7.474%	$172.3131	$172.31	$172.30	$172.30
Purchase #7	$106.38	4.862%	$111.5522	$111.55	$111.55	$111.60
7 purchase totals =	$1,211.32		$1,310.7471	$1,310.74	$1,310.70	$1,310.80