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	$108.65	4.434%	$113.4675	$113.47	$113.45	$113.50
Purchase #2	$124.66	13.437%	$141.4106	$141.41	$141.40	$141.40
Purchase #3	$73.70	13.704%	$83.7998	$83.80	$83.80	$83.80
Purchase #4	$132.47	11.238%	$147.357	$147.36	$147.35	$147.40
Purchase #5	$241.27	7.197%	$258.6342	$258.63	$258.65	$258.60
Purchase #6	$61.46	5.776%	$65.0099	$65.01	$65.00	$65.00
Purchase #7	$28.93	13.674%	$32.8859	$32.89	$32.90	$32.90
7 purchase totals =	$771.14		$842.5649	$842.57	$842.55	$842.60