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	$30.71	5.743%	$32.4737	$32.47	$32.45	$32.50
Purchase #2	$20.66	4.675%	$21.6259	$21.63	$21.65	$21.60
Purchase #3	$131.95	5.532%	$139.2495	$139.25	$139.25	$139.20
Purchase #4	$40.34	13.271%	$45.6935	$45.69	$45.70	$45.70
Purchase #5	$179.50	10.254%	$197.9059	$197.91	$197.90	$197.90
Purchase #6	$45.48	8.318%	$49.263	$49.26	$49.25	$49.30
Purchase #7	$19.26	13.595%	$21.8784	$21.88	$21.90	$21.90
7 purchase totals =	$467.90		$508.0899	$508.09	$508.10	$508.10