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	$79.97	10.717%	$88.5404	$88.54	$88.55	$88.50
Purchase #2	$79.54	4.133%	$82.8274	$82.83	$82.85	$82.80
Purchase #3	$242.77	12.806%	$273.8591	$273.86	$273.85	$273.90
Purchase #4	$87.26	8.320%	$94.52	$94.52	$94.50	$94.50
Purchase #5	$31.67	8.778%	$34.45	$34.45	$34.45	$34.50
Purchase #6	$23.40	9.328%	$25.5828	$25.58	$25.60	$25.60
Purchase #7	$189.57	5.544%	$200.0798	$200.08	$200.10	$200.10
7 purchase totals =	$734.18		$799.8595	$799.86	$799.90	$799.90