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	$100.93	8.460%	$109.4687	$109.47	$109.45	$109.50
Purchase #2	$11.79	4.111%	$12.2747	$12.27	$12.25	$12.30
Purchase #3	$126.90	7.369%	$136.2513	$136.25	$136.25	$136.30
Purchase #4	$137.85	13.421%	$156.3508	$156.35	$156.35	$156.40
Purchase #5	$78.30	3.823%	$81.2934	$81.29	$81.30	$81.30
Purchase #6	$204.64	5.572%	$216.0425	$216.04	$216.05	$216.00
Purchase #7	$124.84	6.210%	$132.5926	$132.59	$132.60	$132.60
7 purchase totals =	$785.25		$844.2740	$844.26	$844.25	$844.40