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	$6.42	6.389%	$6.8302	$6.83	$6.85	$6.80
Purchase #2	$37.76	13.747%	$42.9509	$42.95	$42.95	$43.00
Purchase #3	$245.52	12.225%	$275.5348	$275.53	$275.55	$275.50
Purchase #4	$161.90	3.595%	$167.7203	$167.72	$167.70	$167.70
Purchase #5	$39.47	8.731%	$42.9161	$42.92	$42.90	$42.90
Purchase #6	$123.56	9.318%	$135.0733	$135.07	$135.05	$135.10
Purchase #7	$48.31	11.696%	$53.9603	$53.96	$53.95	$54.00
7 purchase totals =	$662.94		$724.9859	$724.98	$724.95	$725.00