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	$201.43	12.119%	$225.8413	$225.84	$225.85	$225.80
Purchase #2	$32.90	3.656%	$34.1028	$34.10	$34.10	$34.10
Purchase #3	$229.75	9.175%	$250.8296	$250.83	$250.85	$250.80
Purchase #4	$16.39	8.485%	$17.7807	$17.78	$17.80	$17.80
Purchase #5	$59.47	12.544%	$66.9299	$66.93	$66.95	$66.90
Purchase #6	$127.84	12.247%	$143.4966	$143.50	$143.50	$143.50
Purchase #7	$96.43	4.460%	$100.7308	$100.73	$100.75	$100.70
7 purchase totals =	$764.21		$839.7117	$839.71	$839.80	$839.60