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	$33.61	7.272%	$36.0541	$36.05	$36.05	$36.10
Purchase #2	$235.27	5.363%	$247.8875	$247.89	$247.90	$247.90
Purchase #3	$219.43	9.646%	$240.5962	$240.60	$240.60	$240.60
Purchase #4	$45.45	5.302%	$47.8598	$47.86	$47.85	$47.90
Purchase #5	$108.58	4.851%	$113.8472	$113.85	$113.85	$113.80
Purchase #6	$50.93	4.196%	$53.067	$53.07	$53.05	$53.10
Purchase #7	$133.27	3.510%	$137.9478	$137.95	$137.95	$137.90
7 purchase totals =	$826.54		$877.2596	$877.27	$877.25	$877.30