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	$233.27	11.709%	$260.5836	$260.58	$260.60	$260.60
Purchase #2	$89.63	11.405%	$99.8523	$99.85	$99.85	$99.90
Purchase #3	$92.66	12.161%	$103.9284	$103.93	$103.95	$103.90
Purchase #4	$152.62	10.497%	$168.6405	$168.64	$168.65	$168.60
Purchase #5	$155.95	8.104%	$168.5882	$168.59	$168.60	$168.60
Purchase #6	$86.94	5.318%	$91.5635	$91.56	$91.55	$91.60
Purchase #7	$42.78	13.235%	$48.4419	$48.44	$48.45	$48.40
7 purchase totals =	$853.85		$941.5984	$941.59	$941.65	$941.60