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	$90.80	11.796%	$101.5108	$101.51	$101.50	$101.50
Purchase #2	$37.89	3.724%	$39.301	$39.30	$39.30	$39.30
Purchase #3	$158.42	13.677%	$180.0871	$180.09	$180.10	$180.10
Purchase #4	$67.51	10.517%	$74.61	$74.61	$74.60	$74.60
Purchase #5	$71.76	6.845%	$76.672	$76.67	$76.65	$76.70
Purchase #6	$171.73	11.738%	$191.8877	$191.89	$191.90	$191.90
Purchase #7	$243.96	5.227%	$256.7118	$256.71	$256.70	$256.70
7 purchase totals =	$842.07		$920.7804	$920.78	$920.75	$920.80