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	$139.45	8.194%	$150.8765	$150.88	$150.90	$150.90
Purchase #2	$82.66	3.517%	$85.5672	$85.57	$85.55	$85.60
Purchase #3	$23.57	6.248%	$25.0427	$25.04	$25.05	$25.00
Purchase #4	$19.50	11.696%	$21.7807	$21.78	$21.80	$21.80
Purchase #5	$225.78	5.547%	$238.304	$238.30	$238.30	$238.30
Purchase #6	$15.86	7.240%	$17.0083	$17.01	$17.00	$17.00
Purchase #7	$72.48	8.536%	$78.6669	$78.67	$78.65	$78.70
7 purchase totals =	$579.30		$617.2463	$617.25	$617.25	$617.30