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	$29.70	10.732%	$32.8874	$32.89	$32.90	$32.90
Purchase #2	$37.83	6.380%	$40.2436	$40.24	$40.25	$40.20
Purchase #3	$111.35	12.268%	$125.0104	$125.01	$125.00	$125.00
Purchase #4	$37.63	5.577%	$39.7286	$39.73	$39.75	$39.70
Purchase #5	$138.66	5.474%	$146.2502	$146.25	$146.25	$146.30
Purchase #6	$137.71	7.124%	$147.5205	$147.52	$147.50	$147.50
Purchase #7	$173.52	6.686%	$185.1215	$185.12	$185.10	$185.10
7 purchase totals =	$666.40		$716.7622	$716.76	$716.75	$716.70