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	$47.92	9.390%	$52.4197	$52.42	$52.40	$52.40
Purchase #2	$38.45	3.333%	$39.7315	$39.73	$39.75	$39.70
Purchase #3	$16.90	11.612%	$18.8624	$18.86	$18.85	$18.90
Purchase #4	$223.64	13.427%	$253.6681	$253.67	$253.65	$253.70
Purchase #5	$108.29	3.430%	$112.0043	$112.00	$112.00	$112.00
Purchase #6	$64.80	10.862%	$71.8386	$71.84	$71.85	$71.80
Purchase #7	$150.46	8.287%	$162.9286	$162.93	$162.95	$162.90
7 purchase totals =	$650.46		$711.4532	$711.45	$711.45	$711.40