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	$30.86	3.731%	$32.0114	$32.01	$32.00	$32.00
Purchase #2	$211.65	12.836%	$238.8174	$238.82	$238.80	$238.80
Purchase #3	$67.28	7.824%	$72.544	$72.54	$72.55	$72.50
Purchase #4	$214.79	3.708%	$222.7544	$222.75	$222.75	$222.80
Purchase #5	$225.58	7.738%	$243.0354	$243.04	$243.05	$243.00
Purchase #6	$62.39	4.642%	$65.2861	$65.29	$65.30	$65.30
Purchase #7	$61.97	7.330%	$66.5124	$66.51	$66.50	$66.50
7 purchase totals =	$874.52		$940.9611	$940.96	$940.95	$940.90