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	$52.90	3.779%	$54.8991	$54.90	$54.90	$54.90
Purchase #2	$135.79	7.356%	$145.7787	$145.78	$145.80	$145.80
Purchase #3	$74.78	4.774%	$78.35	$78.35	$78.35	$78.40
Purchase #4	$94.77	7.305%	$101.6929	$101.69	$101.70	$101.70
Purchase #5	$113.60	11.711%	$126.9037	$126.90	$126.90	$126.90
Purchase #6	$203.89	6.849%	$217.8544	$217.85	$217.85	$217.90
Purchase #7	$135.95	7.472%	$146.1082	$146.11	$146.10	$146.10
7 purchase totals =	$811.68		$871.5870	$871.58	$871.60	$871.70