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	$82.61	9.221%	$90.2275	$90.23	$90.25	$90.20
Purchase #2	$78.58	3.451%	$81.2918	$81.29	$81.30	$81.30
Purchase #3	$65.56	8.537%	$71.1569	$71.16	$71.15	$71.20
Purchase #4	$227.27	5.414%	$239.5744	$239.57	$239.55	$239.60
Purchase #5	$95.71	13.392%	$108.5275	$108.53	$108.55	$108.50
Purchase #6	$153.90	9.728%	$168.8714	$168.87	$168.85	$168.90
Purchase #7	$169.79	5.864%	$179.7465	$179.75	$179.75	$179.70
7 purchase totals =	$873.42		$939.3960	$939.40	$939.40	$939.40