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	$102.94	6.219%	$109.3418	$109.34	$109.35	$109.30
Purchase #2	$239.61	3.153%	$247.1649	$247.16	$247.15	$247.20
Purchase #3	$110.32	7.602%	$118.7065	$118.71	$118.70	$118.70
Purchase #4	$108.97	13.332%	$123.4979	$123.50	$123.50	$123.50
Purchase #5	$67.58	12.540%	$76.0545	$76.05	$76.05	$76.10
Purchase #6	$66.36	6.724%	$70.822	$70.82	$70.80	$70.80
Purchase #7	$83.80	6.371%	$89.1389	$89.14	$89.15	$89.10
7 purchase totals =	$779.58		$834.7265	$834.72	$834.70	$834.70