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	$48.39	5.457%	$51.0306	$51.03	$51.05	$51.00
Purchase #2	$125.82	12.544%	$141.6029	$141.60	$141.60	$141.60
Purchase #3	$83.69	7.382%	$89.868	$89.87	$89.85	$89.90
Purchase #4	$162.35	9.352%	$177.533	$177.53	$177.55	$177.50
Purchase #5	$44.78	13.247%	$50.712	$50.71	$50.70	$50.70
Purchase #6	$236.28	11.371%	$263.1474	$263.15	$263.15	$263.10
Purchase #7	$44.82	13.127%	$50.7035	$50.70	$50.70	$50.70
7 purchase totals =	$746.13		$824.5974	$824.59	$824.60	$824.50