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	$35.65	5.293%	$37.537	$37.54	$37.55	$37.50
Purchase #2	$143.28	5.262%	$150.8194	$150.82	$150.80	$150.80
Purchase #3	$173.40	8.868%	$188.7771	$188.78	$188.80	$188.80
Purchase #4	$249.31	4.549%	$260.6511	$260.65	$260.65	$260.70
Purchase #5	$57.96	7.811%	$62.4873	$62.49	$62.50	$62.50
Purchase #6	$16.38	10.550%	$18.1081	$18.11	$18.10	$18.10
Purchase #7	$43.96	13.764%	$50.0107	$50.01	$50.00	$50.00
7 purchase totals =	$719.94		$768.3907	$768.40	$768.40	$768.40