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	$186.67	13.377%	$211.6408	$211.64	$211.65	$211.60
Purchase #2	$168.44	12.606%	$189.6735	$189.67	$189.65	$189.70
Purchase #3	$199.25	4.816%	$208.8459	$208.85	$208.85	$208.80
Purchase #4	$122.81	4.734%	$128.6238	$128.62	$128.60	$128.60
Purchase #5	$40.89	10.295%	$45.0996	$45.10	$45.10	$45.10
Purchase #6	$73.64	13.291%	$83.4275	$83.43	$83.45	$83.40
Purchase #7	$85.81	5.601%	$90.6162	$90.62	$90.60	$90.60
7 purchase totals =	$877.51		$957.9273	$957.93	$957.90	$957.80