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	$68.84	12.306%	$77.3115	$77.31	$77.30	$77.30
Purchase #2	$53.95	10.103%	$59.4006	$59.40	$59.40	$59.40
Purchase #3	$72.60	5.423%	$76.5371	$76.54	$76.55	$76.50
Purchase #4	$205.91	12.677%	$232.0132	$232.01	$232.00	$232.00
Purchase #5	$36.82	9.436%	$40.2943	$40.29	$40.30	$40.30
Purchase #6	$39.73	6.340%	$42.2489	$42.25	$42.25	$42.20
Purchase #7	$137.34	10.574%	$151.8623	$151.86	$151.85	$151.90
7 purchase totals =	$615.19		$679.6679	$679.66	$679.65	$679.60