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	$40.69	3.553%	$42.1357	$42.14	$42.15	$42.10
Purchase #2	$32.40	6.763%	$34.5912	$34.59	$34.60	$34.60
Purchase #3	$10.80	3.404%	$11.1676	$11.17	$11.15	$11.20
Purchase #4	$135.72	9.665%	$148.8373	$148.84	$148.85	$148.80
Purchase #5	$89.34	5.650%	$94.3877	$94.39	$94.40	$94.40
Purchase #6	$142.43	4.582%	$148.9561	$148.96	$148.95	$149.00
Purchase #7	$143.30	3.547%	$148.3829	$148.38	$148.40	$148.40
7 purchase totals =	$594.68		$628.4585	$628.47	$628.50	$628.50