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	$127.83	4.570%	$133.6718	$133.67	$133.65	$133.70
Purchase #2	$126.95	8.358%	$137.5605	$137.56	$137.55	$137.60
Purchase #3	$45.65	11.493%	$50.8966	$50.90	$50.90	$50.90
Purchase #4	$129.84	7.161%	$139.1378	$139.14	$139.15	$139.10
Purchase #5	$37.53	13.828%	$42.7196	$42.72	$42.70	$42.70
Purchase #6	$82.76	3.319%	$85.5068	$85.51	$85.50	$85.50
Purchase #7	$178.53	13.223%	$202.137	$202.14	$202.15	$202.10
7 purchase totals =	$729.09		$791.6301	$791.64	$791.60	$791.60