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	$67.60	11.188%	$75.1631	$75.16	$75.15	$75.20
Purchase #2	$143.66	6.367%	$152.8068	$152.81	$152.80	$152.80
Purchase #3	$27.74	13.398%	$31.4566	$31.46	$31.45	$31.50
Purchase #4	$221.62	3.571%	$229.5341	$229.53	$229.55	$229.50
Purchase #5	$152.70	6.244%	$162.2346	$162.23	$162.25	$162.20
Purchase #6	$127.52	13.236%	$144.3985	$144.40	$144.40	$144.40
Purchase #7	$172.66	7.845%	$186.2052	$186.21	$186.20	$186.20
7 purchase totals =	$913.50		$981.7989	$981.80	$981.80	$981.80