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	$80.39	13.110%	$90.9291	$90.93	$90.95	$90.90
Purchase #2	$75.52	4.456%	$78.8852	$78.89	$78.90	$78.90
Purchase #3	$91.35	12.340%	$102.6226	$102.62	$102.60	$102.60
Purchase #4	$224.53	3.221%	$231.7621	$231.76	$231.75	$231.80
Purchase #5	$154.89	13.198%	$175.3324	$175.33	$175.35	$175.30
Purchase #6	$15.76	9.248%	$17.2175	$17.22	$17.20	$17.20
Purchase #7	$7.30	8.305%	$7.9063	$7.91	$7.90	$7.90
7 purchase totals =	$649.74		$704.6552	$704.66	$704.65	$704.60