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	$36.53	7.655%	$39.3264	$39.33	$39.35	$39.30
Purchase #2	$159.70	3.546%	$165.363	$165.36	$165.35	$165.40
Purchase #3	$34.83	8.593%	$37.8229	$37.82	$37.80	$37.80
Purchase #4	$158.57	12.401%	$178.2343	$178.23	$178.25	$178.20
Purchase #5	$68.72	12.677%	$77.4316	$77.43	$77.45	$77.40
Purchase #6	$106.71	13.316%	$120.9195	$120.92	$120.90	$120.90
Purchase #7	$144.61	10.301%	$159.5063	$159.51	$159.50	$159.50
7 purchase totals =	$709.67		$778.6040	$778.60	$778.60	$778.50