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	$50.71	9.185%	$55.3677	$55.37	$55.35	$55.40
Purchase #2	$140.30	12.343%	$157.6172	$157.62	$157.60	$157.60
Purchase #3	$147.53	3.626%	$152.8794	$152.88	$152.90	$152.90
Purchase #4	$232.48	13.725%	$264.3879	$264.39	$264.40	$264.40
Purchase #5	$225.56	12.466%	$253.6783	$253.68	$253.70	$253.70
Purchase #6	$164.55	6.825%	$175.7805	$175.78	$175.80	$175.80
Purchase #7	$172.34	13.785%	$196.0971	$196.10	$196.10	$196.10
7 purchase totals =	$1,133.47		$1,255.8081	$1,255.82	$1,255.85	$1,255.90