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	$239.83	6.454%	$255.3086	$255.31	$255.30	$255.30
Purchase #2	$98.75	13.426%	$112.0082	$112.01	$112.00	$112.00
Purchase #3	$100.29	3.342%	$103.6417	$103.64	$103.65	$103.60
Purchase #4	$20.26	12.116%	$22.7147	$22.71	$22.70	$22.70
Purchase #5	$153.84	11.153%	$170.9978	$171.00	$171.00	$171.00
Purchase #6	$36.33	3.256%	$37.5129	$37.51	$37.50	$37.50
Purchase #7	$217.83	4.632%	$227.9199	$227.92	$227.90	$227.90
7 purchase totals =	$867.13		$930.1038	$930.10	$930.05	$930.00