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	$126.59	8.654%	$137.5451	$137.55	$137.55	$137.50
Purchase #2	$79.75	12.406%	$89.6438	$89.64	$89.65	$89.60
Purchase #3	$23.42	6.134%	$24.8566	$24.86	$24.85	$24.90
Purchase #4	$145.67	9.771%	$159.9034	$159.90	$159.90	$159.90
Purchase #5	$82.35	9.695%	$90.3338	$90.33	$90.35	$90.30
Purchase #6	$27.63	6.646%	$29.4663	$29.47	$29.45	$29.50
Purchase #7	$160.95	6.184%	$170.9031	$170.90	$170.90	$170.90
7 purchase totals =	$646.36		$702.6521	$702.65	$702.65	$702.60