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	$172.57	6.589%	$183.9406	$183.94	$183.95	$183.90
Purchase #2	$220.72	8.227%	$238.8786	$238.88	$238.90	$238.90
Purchase #3	$73.89	13.215%	$83.6546	$83.65	$83.65	$83.70
Purchase #4	$36.76	10.445%	$40.5996	$40.60	$40.60	$40.60
Purchase #5	$75.34	13.160%	$85.2547	$85.25	$85.25	$85.30
Purchase #6	$231.51	8.590%	$251.3967	$251.40	$251.40	$251.40
Purchase #7	$181.60	8.332%	$196.7309	$196.73	$196.75	$196.70
7 purchase totals =	$992.39		$1,080.4557	$1,080.45	$1,080.50	$1,080.50