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	$225.85	12.323%	$253.6815	$253.68	$253.70	$253.70
Purchase #2	$87.79	9.724%	$96.3267	$96.33	$96.35	$96.30
Purchase #3	$190.92	12.776%	$215.3119	$215.31	$215.30	$215.30
Purchase #4	$243.34	5.267%	$256.1567	$256.16	$256.15	$256.20
Purchase #5	$140.93	3.198%	$145.4369	$145.44	$145.45	$145.40
Purchase #6	$64.75	12.371%	$72.7602	$72.76	$72.75	$72.80
Purchase #7	$23.29	3.686%	$24.1485	$24.15	$24.15	$24.10
7 purchase totals =	$976.87		$1,063.8224	$1,063.83	$1,063.85	$1,063.80