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	$36.34	5.841%	$38.4626	$38.46	$38.45	$38.50
Purchase #2	$190.43	4.821%	$199.6106	$199.61	$199.60	$199.60
Purchase #3	$147.60	11.793%	$165.0065	$165.01	$165.00	$165.00
Purchase #4	$169.70	11.119%	$188.5689	$188.57	$188.55	$188.60
Purchase #5	$189.38	12.268%	$212.6131	$212.61	$212.60	$212.60
Purchase #6	$80.55	12.385%	$90.5261	$90.53	$90.55	$90.50
Purchase #7	$42.29	3.678%	$43.8454	$43.85	$43.85	$43.80
7 purchase totals =	$856.29		$938.6332	$938.64	$938.60	$938.60