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	$40.57	11.697%	$45.3155	$45.32	$45.30	$45.30
Purchase #2	$112.76	5.800%	$119.3001	$119.30	$119.30	$119.30
Purchase #3	$40.72	10.677%	$45.0677	$45.07	$45.05	$45.10
Purchase #4	$149.70	3.565%	$155.0368	$155.04	$155.05	$155.00
Purchase #5	$146.52	10.693%	$162.1874	$162.19	$162.20	$162.20
Purchase #6	$87.92	4.431%	$91.8157	$91.82	$91.80	$91.80
Purchase #7	$34.46	12.591%	$38.7989	$38.80	$38.80	$38.80
7 purchase totals =	$612.65		$657.5221	$657.54	$657.50	$657.50