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	$50.58	12.802%	$57.0553	$57.06	$57.05	$57.10
Purchase #2	$105.59	6.544%	$112.4998	$112.50	$112.50	$112.50
Purchase #3	$144.28	5.691%	$152.491	$152.49	$152.50	$152.50
Purchase #4	$12.53	8.640%	$13.6126	$13.61	$13.60	$13.60
Purchase #5	$151.54	11.111%	$168.3776	$168.38	$168.40	$168.40
Purchase #6	$240.50	6.282%	$255.6082	$255.61	$255.60	$255.60
Purchase #7	$69.77	8.300%	$75.5609	$75.56	$75.55	$75.60
7 purchase totals =	$774.79		$835.2054	$835.21	$835.20	$835.30