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	$139.82	13.666%	$158.9278	$158.93	$158.95	$158.90
Purchase #2	$74.76	9.237%	$81.6656	$81.67	$81.65	$81.70
Purchase #3	$46.84	6.851%	$50.049	$50.05	$50.05	$50.00
Purchase #4	$33.45	9.701%	$36.695	$36.70	$36.70	$36.70
Purchase #5	$59.49	3.183%	$61.3836	$61.38	$61.40	$61.40
Purchase #6	$50.46	7.533%	$54.2612	$54.26	$54.25	$54.30
Purchase #7	$72.98	7.619%	$78.5403	$78.54	$78.55	$78.50
7 purchase totals =	$477.80		$521.5225	$521.53	$521.55	$521.50