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	$56.90	9.189%	$62.1285	$62.13	$62.15	$62.10
Purchase #2	$140.48	7.171%	$150.5538	$150.55	$150.55	$150.60
Purchase #3	$196.61	10.245%	$216.7527	$216.75	$216.75	$216.80
Purchase #4	$81.56	6.210%	$86.6249	$86.62	$86.60	$86.60
Purchase #5	$21.86	12.690%	$24.634	$24.63	$24.65	$24.60
Purchase #6	$144.50	10.256%	$159.3199	$159.32	$159.30	$159.30
Purchase #7	$62.81	12.847%	$70.8792	$70.88	$70.90	$70.90
7 purchase totals =	$704.72		$770.8930	$770.88	$770.90	$770.90