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	$76.89	13.274%	$87.0964	$87.10	$87.10	$87.10
Purchase #2	$183.61	9.362%	$200.7996	$200.80	$200.80	$200.80
Purchase #3	$162.29	4.337%	$169.3285	$169.33	$169.35	$169.30
Purchase #4	$89.57	5.802%	$94.7669	$94.77	$94.75	$94.80
Purchase #5	$64.54	3.645%	$66.8925	$66.89	$66.90	$66.90
Purchase #6	$125.88	9.211%	$137.4748	$137.47	$137.45	$137.50
Purchase #7	$139.37	4.521%	$145.6709	$145.67	$145.65	$145.70
7 purchase totals =	$842.15		$902.0296	$902.03	$902.00	$902.10