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	$68.51	6.103%	$72.6912	$72.69	$72.70	$72.70
Purchase #2	$97.86	3.383%	$101.1706	$101.17	$101.15	$101.20
Purchase #3	$195.25	7.309%	$209.5208	$209.52	$209.50	$209.50
Purchase #4	$196.71	11.812%	$219.9454	$219.95	$219.95	$219.90
Purchase #5	$46.56	3.287%	$48.0904	$48.09	$48.10	$48.10
Purchase #6	$151.84	11.839%	$169.8163	$169.82	$169.80	$169.80
Purchase #7	$165.53	4.222%	$172.5187	$172.52	$172.50	$172.50
7 purchase totals =	$922.26		$993.7534	$993.76	$993.70	$993.70