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	$9.94	9.341%	$10.8685	$10.87	$10.85	$10.90
Purchase #2	$37.61	11.481%	$41.928	$41.93	$41.95	$41.90
Purchase #3	$231.25	10.652%	$255.8828	$255.88	$255.90	$255.90
Purchase #4	$181.43	5.134%	$190.7446	$190.74	$190.75	$190.70
Purchase #5	$222.76	10.120%	$245.3033	$245.30	$245.30	$245.30
Purchase #6	$81.42	13.400%	$92.3303	$92.33	$92.35	$92.30
Purchase #7	$169.81	12.682%	$191.3453	$191.35	$191.35	$191.30
7 purchase totals =	$934.22		$1,028.4028	$1,028.40	$1,028.45	$1,028.30