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	$18.37	7.789%	$19.8008	$19.80	$19.80	$19.80
Purchase #2	$141.77	6.123%	$150.4506	$150.45	$150.45	$150.50
Purchase #3	$6.92	6.650%	$7.3802	$7.38	$7.40	$7.40
Purchase #4	$79.67	11.210%	$88.601	$88.60	$88.60	$88.60
Purchase #5	$124.73	10.484%	$137.8067	$137.81	$137.80	$137.80
Purchase #6	$94.41	5.267%	$99.3826	$99.38	$99.40	$99.40
Purchase #7	$145.59	13.487%	$165.2257	$165.23	$165.25	$165.20
7 purchase totals =	$611.46		$668.6476	$668.65	$668.70	$668.70