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	$31.32	3.707%	$32.481	$32.48	$32.50	$32.50
Purchase #2	$209.53	13.807%	$238.4598	$238.46	$238.45	$238.50
Purchase #3	$56.32	6.534%	$59.9999	$60.00	$60.00	$60.00
Purchase #4	$65.62	12.477%	$73.8074	$73.81	$73.80	$73.80
Purchase #5	$199.94	12.621%	$225.1744	$225.17	$225.15	$225.20
Purchase #6	$114.61	13.697%	$130.3081	$130.31	$130.30	$130.30
Purchase #7	$38.55	10.517%	$42.6043	$42.60	$42.60	$42.60
7 purchase totals =	$715.89		$802.8349	$802.83	$802.80	$802.90