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	$249.34	13.732%	$283.5794	$283.58	$283.60	$283.60
Purchase #2	$202.52	13.340%	$229.5362	$229.54	$229.55	$229.50
Purchase #3	$165.96	10.426%	$183.263	$183.26	$183.25	$183.30
Purchase #4	$85.53	4.713%	$89.561	$89.56	$89.55	$89.60
Purchase #5	$196.57	12.367%	$220.8798	$220.88	$220.90	$220.90
Purchase #6	$45.45	10.508%	$50.2259	$50.23	$50.25	$50.20
Purchase #7	$183.66	8.173%	$198.6705	$198.67	$198.65	$198.70
7 purchase totals =	$1,129.03		$1,255.7158	$1,255.72	$1,255.75	$1,255.80