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	$125.96	9.511%	$137.9401	$137.94	$137.95	$137.90
Purchase #2	$93.63	6.382%	$99.6055	$99.61	$99.60	$99.60
Purchase #3	$114.48	8.873%	$124.6378	$124.64	$124.65	$124.60
Purchase #4	$63.56	11.244%	$70.7067	$70.71	$70.70	$70.70
Purchase #5	$234.56	6.836%	$250.5945	$250.59	$250.60	$250.60
Purchase #6	$20.41	5.593%	$21.5515	$21.55	$21.55	$21.60
Purchase #7	$40.67	4.759%	$42.6055	$42.61	$42.60	$42.60
7 purchase totals =	$693.27		$747.6416	$747.65	$747.65	$747.60