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	$10.41	10.246%	$11.4766	$11.48	$11.50	$11.50
Purchase #2	$95.47	10.362%	$105.3626	$105.36	$105.35	$105.40
Purchase #3	$5.57	12.290%	$6.2546	$6.25	$6.25	$6.30
Purchase #4	$130.65	8.236%	$141.4103	$141.41	$141.40	$141.40
Purchase #5	$19.34	6.496%	$20.5963	$20.60	$20.60	$20.60
Purchase #6	$206.30	5.801%	$218.2675	$218.27	$218.25	$218.30
Purchase #7	$132.45	7.248%	$142.05	$142.05	$142.05	$142.10
7 purchase totals =	$600.19		$645.4179	$645.42	$645.40	$645.60