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	$114.85	5.105%	$120.7131	$120.71	$120.70	$120.70
Purchase #2	$216.61	6.464%	$230.6117	$230.61	$230.60	$230.60
Purchase #3	$57.52	9.331%	$62.8872	$62.89	$62.90	$62.90
Purchase #4	$58.67	10.327%	$64.7289	$64.73	$64.75	$64.70
Purchase #5	$140.32	13.509%	$159.2758	$159.28	$159.30	$159.30
Purchase #6	$78.48	9.812%	$86.1805	$86.18	$86.20	$86.20
Purchase #7	$63.85	13.193%	$72.2737	$72.27	$72.25	$72.30
7 purchase totals =	$730.30		$796.6709	$796.67	$796.70	$796.70