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	$85.57	5.588%	$90.3517	$90.35	$90.35	$90.40
Purchase #2	$90.31	4.644%	$94.504	$94.50	$94.50	$94.50
Purchase #3	$45.87	5.756%	$48.5103	$48.51	$48.50	$48.50
Purchase #4	$140.64	11.198%	$156.3889	$156.39	$156.40	$156.40
Purchase #5	$227.25	11.544%	$253.4837	$253.48	$253.50	$253.50
Purchase #6	$223.81	13.657%	$254.3757	$254.38	$254.40	$254.40
Purchase #7	$28.66	6.649%	$30.5656	$30.57	$30.55	$30.60
7 purchase totals =	$842.11		$928.1799	$928.18	$928.20	$928.30