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	$78.56	9.297%	$85.8637	$85.86	$85.85	$85.90
Purchase #2	$141.92	13.734%	$161.4113	$161.41	$161.40	$161.40
Purchase #3	$246.96	7.233%	$264.8226	$264.82	$264.80	$264.80
Purchase #4	$37.26	12.866%	$42.0539	$42.05	$42.05	$42.10
Purchase #5	$217.64	12.622%	$245.1105	$245.11	$245.10	$245.10
Purchase #6	$246.85	10.119%	$271.8288	$271.83	$271.85	$271.80
Purchase #7	$33.40	4.220%	$34.8095	$34.81	$34.80	$34.80
7 purchase totals =	$1,002.59		$1,105.9003	$1,105.89	$1,105.85	$1,105.90