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	$85.60	5.225%	$90.0726	$90.07	$90.05	$90.10
Purchase #2	$78.70	6.287%	$83.6479	$83.65	$83.65	$83.60
Purchase #3	$158.41	4.493%	$165.5274	$165.53	$165.55	$165.50
Purchase #4	$118.79	11.179%	$132.0695	$132.07	$132.05	$132.10
Purchase #5	$128.44	6.400%	$136.6602	$136.66	$136.65	$136.70
Purchase #6	$126.74	4.417%	$132.3381	$132.34	$132.35	$132.30
Purchase #7	$87.38	5.218%	$91.9395	$91.94	$91.95	$91.90
7 purchase totals =	$784.06		$832.2552	$832.26	$832.25	$832.20