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	$15.61	8.175%	$16.8861	$16.89	$16.90	$16.90
Purchase #2	$132.49	11.578%	$147.8297	$147.83	$147.85	$147.80
Purchase #3	$81.27	10.382%	$89.7075	$89.71	$89.70	$89.70
Purchase #4	$174.52	11.848%	$195.1971	$195.20	$195.20	$195.20
Purchase #5	$180.93	5.818%	$191.4565	$191.46	$191.45	$191.50
Purchase #6	$28.58	8.796%	$31.0939	$31.09	$31.10	$31.10
Purchase #7	$152.31	12.674%	$171.6138	$171.61	$171.60	$171.60
7 purchase totals =	$765.71		$843.7846	$843.79	$843.80	$843.80