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	$168.46	13.128%	$190.5754	$190.58	$190.60	$190.60
Purchase #2	$246.76	10.454%	$272.5563	$272.56	$272.55	$272.60
Purchase #3	$209.25	7.709%	$225.3811	$225.38	$225.40	$225.40
Purchase #4	$78.40	9.188%	$85.6034	$85.60	$85.60	$85.60
Purchase #5	$69.64	7.695%	$74.9988	$75.00	$75.00	$75.00
Purchase #6	$87.59	10.153%	$96.483	$96.48	$96.50	$96.50
Purchase #7	$46.56	8.141%	$50.3504	$50.35	$50.35	$50.40
7 purchase totals =	$906.66		$995.9484	$995.95	$996.00	$996.10