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	$177.92	12.430%	$200.0355	$200.04	$200.05	$200.00
Purchase #2	$129.83	8.763%	$141.207	$141.21	$141.20	$141.20
Purchase #3	$43.96	4.272%	$45.838	$45.84	$45.85	$45.80
Purchase #4	$68.59	12.157%	$76.9285	$76.93	$76.95	$76.90
Purchase #5	$219.32	4.285%	$228.7179	$228.72	$228.70	$228.70
Purchase #6	$59.52	10.321%	$65.6631	$65.66	$65.65	$65.70
Purchase #7	$7.52	5.673%	$7.9466	$7.95	$7.95	$7.90
7 purchase totals =	$706.66		$766.3366	$766.35	$766.35	$766.20