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	$80.77	12.223%	$90.6425	$90.64	$90.65	$90.60
Purchase #2	$123.34	8.790%	$134.1816	$134.18	$134.20	$134.20
Purchase #3	$55.71	10.386%	$61.496	$61.50	$61.50	$61.50
Purchase #4	$132.60	8.463%	$143.8219	$143.82	$143.80	$143.80
Purchase #5	$49.27	3.239%	$50.8659	$50.87	$50.85	$50.90
Purchase #6	$47.71	6.402%	$50.7644	$50.76	$50.75	$50.80
Purchase #7	$133.54	5.742%	$141.2079	$141.21	$141.20	$141.20
7 purchase totals =	$622.94		$672.9802	$672.98	$672.95	$673.00