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	$100.87	12.343%	$113.3204	$113.32	$113.30	$113.30
Purchase #2	$90.85	5.436%	$95.7886	$95.79	$95.80	$95.80
Purchase #3	$152.96	10.338%	$168.773	$168.77	$168.75	$168.80
Purchase #4	$207.60	10.596%	$229.5973	$229.60	$229.60	$229.60
Purchase #5	$134.95	10.141%	$148.6353	$148.64	$148.65	$148.60
Purchase #6	$176.42	9.185%	$192.6242	$192.62	$192.60	$192.60
Purchase #7	$129.73	6.204%	$137.7784	$137.78	$137.80	$137.80
7 purchase totals =	$993.38		$1,086.5172	$1,086.52	$1,086.50	$1,086.50