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	$231.83	3.683%	$240.3683	$240.37	$240.35	$240.40
Purchase #2	$52.25	13.437%	$59.2708	$59.27	$59.25	$59.30
Purchase #3	$91.64	6.497%	$97.5939	$97.59	$97.60	$97.60
Purchase #4	$64.82	3.425%	$67.0401	$67.04	$67.05	$67.00
Purchase #5	$193.60	6.809%	$206.7822	$206.78	$206.80	$206.80
Purchase #6	$115.72	10.646%	$128.0396	$128.04	$128.05	$128.00
Purchase #7	$146.52	7.501%	$157.5105	$157.51	$157.50	$157.50
7 purchase totals =	$896.38		$956.6054	$956.60	$956.60	$956.60