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	$217.48	10.596%	$240.5242	$240.52	$240.50	$240.50
Purchase #2	$131.78	7.791%	$142.047	$142.05	$142.05	$142.00
Purchase #3	$88.43	7.334%	$94.9155	$94.92	$94.90	$94.90
Purchase #4	$69.70	3.835%	$72.373	$72.37	$72.35	$72.40
Purchase #5	$189.62	5.138%	$199.3627	$199.36	$199.35	$199.40
Purchase #6	$100.67	13.718%	$114.4799	$114.48	$114.50	$114.50
Purchase #7	$6.35	12.699%	$7.1564	$7.16	$7.15	$7.20
7 purchase totals =	$804.03		$870.8587	$870.86	$870.80	$870.90