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	$115.98	13.846%	$132.0386	$132.04	$132.05	$132.00
Purchase #2	$82.64	9.622%	$90.5916	$90.59	$90.60	$90.60
Purchase #3	$67.40	3.511%	$69.7664	$69.77	$69.75	$69.80
Purchase #4	$5.60	5.217%	$5.8922	$5.89	$5.90	$5.90
Purchase #5	$83.93	12.747%	$94.6286	$94.63	$94.65	$94.60
Purchase #6	$211.32	8.201%	$228.6504	$228.65	$228.65	$228.70
Purchase #7	$18.54	12.634%	$20.8823	$20.88	$20.90	$20.90
7 purchase totals =	$585.41		$642.4501	$642.45	$642.50	$642.50