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	$35.72	6.211%	$37.9386	$37.94	$37.95	$37.90
Purchase #2	$144.54	12.339%	$162.3748	$162.37	$162.35	$162.40
Purchase #3	$199.58	13.626%	$226.7748	$226.77	$226.75	$226.80
Purchase #4	$74.90	11.159%	$83.2581	$83.26	$83.25	$83.30
Purchase #5	$39.26	3.249%	$40.5356	$40.54	$40.55	$40.50
Purchase #6	$170.26	3.666%	$176.5017	$176.50	$176.50	$176.50
Purchase #7	$80.30	3.626%	$83.2117	$83.21	$83.20	$83.20
7 purchase totals =	$744.56		$810.5953	$810.59	$810.55	$810.60