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	$77.58	7.227%	$83.1867	$83.19	$83.20	$83.20
Purchase #2	$133.87	5.577%	$141.3359	$141.34	$141.35	$141.30
Purchase #3	$250.52	6.540%	$266.904	$266.90	$266.90	$266.90
Purchase #4	$186.67	5.491%	$196.92	$196.92	$196.90	$196.90
Purchase #5	$29.88	5.309%	$31.4663	$31.47	$31.45	$31.50
Purchase #6	$88.40	12.698%	$99.625	$99.63	$99.65	$99.60
Purchase #7	$124.37	13.750%	$141.4709	$141.47	$141.45	$141.50
7 purchase totals =	$891.29		$960.9088	$960.92	$960.90	$960.90