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	$50.57	4.230%	$52.7091	$52.71	$52.70	$52.70
Purchase #2	$104.38	12.675%	$117.6102	$117.61	$117.60	$117.60
Purchase #3	$198.51	12.264%	$222.8553	$222.86	$222.85	$222.90
Purchase #4	$85.57	11.429%	$95.3498	$95.35	$95.35	$95.30
Purchase #5	$124.94	13.698%	$142.0543	$142.05	$142.05	$142.10
Purchase #6	$42.44	8.120%	$45.8861	$45.89	$45.90	$45.90
Purchase #7	$188.98	8.363%	$204.7844	$204.78	$204.80	$204.80
7 purchase totals =	$795.39		$881.2492	$881.25	$881.25	$881.30