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	$133.56	6.632%	$142.4177	$142.42	$142.40	$142.40
Purchase #2	$60.37	11.185%	$67.1224	$67.12	$67.10	$67.10
Purchase #3	$78.81	8.420%	$85.4458	$85.45	$85.45	$85.40
Purchase #4	$161.68	7.412%	$173.6637	$173.66	$173.65	$173.70
Purchase #5	$59.63	13.796%	$67.8566	$67.86	$67.85	$67.90
Purchase #6	$225.52	5.671%	$238.3092	$238.31	$238.30	$238.30
Purchase #7	$40.77	3.438%	$42.1717	$42.17	$42.15	$42.20
7 purchase totals =	$760.34		$816.9871	$816.99	$816.90	$817.00