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	$74.86	3.277%	$77.3132	$77.31	$77.30	$77.30
Purchase #2	$72.72	10.191%	$80.1309	$80.13	$80.15	$80.10
Purchase #3	$228.83	11.658%	$255.507	$255.51	$255.50	$255.50
Purchase #4	$121.45	10.285%	$133.9411	$133.94	$133.95	$133.90
Purchase #5	$34.37	9.753%	$37.7221	$37.72	$37.70	$37.70
Purchase #6	$32.55	6.457%	$34.6518	$34.65	$34.65	$34.70
Purchase #7	$124.53	12.788%	$140.4549	$140.45	$140.45	$140.50
7 purchase totals =	$689.31		$759.7210	$759.71	$759.70	$759.70