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	$65.73	8.239%	$71.1455	$71.15	$71.15	$71.10
Purchase #2	$239.54	6.648%	$255.4646	$255.46	$255.45	$255.50
Purchase #3	$170.67	13.864%	$194.3317	$194.33	$194.35	$194.30
Purchase #4	$172.42	10.693%	$190.8569	$190.86	$190.85	$190.90
Purchase #5	$186.78	4.419%	$195.0338	$195.03	$195.05	$195.00
Purchase #6	$88.67	8.554%	$96.2548	$96.25	$96.25	$96.30
Purchase #7	$147.52	5.637%	$155.8357	$155.84	$155.85	$155.80
7 purchase totals =	$1,071.33		$1,158.9230	$1,158.92	$1,158.95	$1,158.90