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	$36.31	10.431%	$40.0975	$40.10	$40.10	$40.10
Purchase #2	$202.89	4.461%	$211.9409	$211.94	$211.95	$211.90
Purchase #3	$213.85	11.389%	$238.2054	$238.21	$238.20	$238.20
Purchase #4	$114.61	5.490%	$120.9021	$120.90	$120.90	$120.90
Purchase #5	$105.47	11.783%	$117.8975	$117.90	$117.90	$117.90
Purchase #6	$18.65	9.829%	$20.4831	$20.48	$20.50	$20.50
Purchase #7	$215.82	6.245%	$229.298	$229.30	$229.30	$229.30
7 purchase totals =	$907.60		$978.8245	$978.83	$978.85	$978.80