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	$135.55	7.603%	$145.8559	$145.86	$145.85	$145.90
Purchase #2	$47.81	10.297%	$52.733	$52.73	$52.75	$52.70
Purchase #3	$18.64	5.223%	$19.6136	$19.61	$19.60	$19.60
Purchase #4	$123.94	12.497%	$139.4288	$139.43	$139.45	$139.40
Purchase #5	$231.69	4.136%	$241.2727	$241.27	$241.25	$241.30
Purchase #6	$231.83	5.258%	$244.0196	$244.02	$244.00	$244.00
Purchase #7	$72.96	7.382%	$78.3459	$78.35	$78.35	$78.30
7 purchase totals =	$862.42		$921.2695	$921.27	$921.25	$921.20