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	$40.53	11.631%	$45.244	$45.24	$45.25	$45.20
Purchase #2	$120.99	13.684%	$137.5463	$137.55	$137.55	$137.50
Purchase #3	$39.56	8.339%	$42.8589	$42.86	$42.85	$42.90
Purchase #4	$32.27	5.345%	$33.9948	$33.99	$34.00	$34.00
Purchase #5	$154.50	3.567%	$160.011	$160.01	$160.00	$160.00
Purchase #6	$92.48	6.619%	$98.6013	$98.60	$98.60	$98.60
Purchase #7	$152.72	5.625%	$161.3105	$161.31	$161.30	$161.30
7 purchase totals =	$633.05		$679.5668	$679.56	$679.55	$679.50