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	$169.28	12.700%	$190.7786	$190.78	$190.80	$190.80
Purchase #2	$59.48	6.788%	$63.5175	$63.52	$63.50	$63.50
Purchase #3	$228.93	4.161%	$238.4558	$238.46	$238.45	$238.50
Purchase #4	$160.90	6.488%	$171.3392	$171.34	$171.35	$171.30
Purchase #5	$18.40	5.737%	$19.4556	$19.46	$19.45	$19.50
Purchase #6	$144.47	13.539%	$164.0298	$164.03	$164.05	$164.00
Purchase #7	$28.70	9.185%	$31.3361	$31.34	$31.35	$31.30
7 purchase totals =	$810.16		$878.9126	$878.93	$878.95	$878.90