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	$126.96	11.515%	$141.5794	$141.58	$141.60	$141.60
Purchase #2	$188.78	6.135%	$200.3617	$200.36	$200.35	$200.40
Purchase #3	$73.95	10.569%	$81.7658	$81.77	$81.75	$81.80
Purchase #4	$250.50	7.439%	$269.1347	$269.13	$269.15	$269.10
Purchase #5	$92.83	7.777%	$100.0494	$100.05	$100.05	$100.00
Purchase #6	$9.29	3.340%	$9.6003	$9.60	$9.60	$9.60
Purchase #7	$37.71	13.724%	$42.8853	$42.89	$42.90	$42.90
7 purchase totals =	$780.02		$845.3766	$845.38	$845.40	$845.40