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	$154.67	6.490%	$164.7081	$164.71	$164.70	$164.70
Purchase #2	$39.85	5.514%	$42.0473	$42.05	$42.05	$42.00
Purchase #3	$93.74	5.322%	$98.7288	$98.73	$98.75	$98.70
Purchase #4	$225.62	6.649%	$240.6215	$240.62	$240.60	$240.60
Purchase #5	$72.43	10.578%	$80.0916	$80.09	$80.10	$80.10
Purchase #6	$197.94	7.389%	$212.5658	$212.57	$212.55	$212.60
Purchase #7	$82.56	8.782%	$89.8104	$89.81	$89.80	$89.80
7 purchase totals =	$866.81		$928.5735	$928.58	$928.55	$928.50