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	$114.30	6.686%	$121.9421	$121.94	$121.95	$121.90
Purchase #2	$222.43	7.427%	$238.9499	$238.95	$238.95	$238.90
Purchase #3	$131.99	5.766%	$139.6005	$139.60	$139.60	$139.60
Purchase #4	$57.45	3.686%	$59.5676	$59.57	$59.55	$59.60
Purchase #5	$50.79	11.193%	$56.4749	$56.47	$56.45	$56.50
Purchase #6	$95.32	7.634%	$102.5967	$102.60	$102.60	$102.60
Purchase #7	$223.28	3.387%	$230.8425	$230.84	$230.85	$230.80
7 purchase totals =	$895.56		$949.9742	$949.97	$949.95	$949.90