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	$45.73	12.196%	$51.3072	$51.31	$51.30	$51.30
Purchase #2	$45.55	11.841%	$50.9436	$50.94	$50.95	$50.90
Purchase #3	$151.27	5.250%	$159.2117	$159.21	$159.20	$159.20
Purchase #4	$139.47	12.475%	$156.8689	$156.87	$156.85	$156.90
Purchase #5	$36.27	11.441%	$40.4197	$40.42	$40.40	$40.40
Purchase #6	$10.69	5.670%	$11.2961	$11.30	$11.30	$11.30
Purchase #7	$85.64	10.867%	$94.9465	$94.95	$94.95	$94.90
7 purchase totals =	$514.62		$564.9937	$565.00	$564.95	$564.90