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	$73.59	13.405%	$83.4547	$83.45	$83.45	$83.50
Purchase #2	$25.46	13.600%	$28.9226	$28.92	$28.90	$28.90
Purchase #3	$227.95	10.130%	$251.0413	$251.04	$251.05	$251.00
Purchase #4	$69.41	4.862%	$72.7847	$72.78	$72.80	$72.80
Purchase #5	$164.82	4.361%	$172.0078	$172.01	$172.00	$172.00
Purchase #6	$178.77	6.322%	$190.0718	$190.07	$190.05	$190.10
Purchase #7	$47.98	7.368%	$51.5152	$51.52	$51.50	$51.50
7 purchase totals =	$787.98		$849.7981	$849.79	$849.75	$849.80