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	$98.74	10.581%	$109.1877	$109.19	$109.20	$109.20
Purchase #2	$214.61	11.754%	$239.8353	$239.84	$239.85	$239.80
Purchase #3	$44.43	3.375%	$45.9295	$45.93	$45.95	$45.90
Purchase #4	$230.35	13.212%	$260.7838	$260.78	$260.80	$260.80
Purchase #5	$196.27	13.348%	$222.4681	$222.47	$222.45	$222.50
Purchase #6	$36.46	8.459%	$39.5442	$39.54	$39.55	$39.50
Purchase #7	$79.86	12.340%	$89.7147	$89.71	$89.70	$89.70
7 purchase totals =	$900.72		$1,007.4633	$1,007.46	$1,007.50	$1,007.40