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	$134.85	3.117%	$139.0533	$139.05	$139.05	$139.10
Purchase #2	$185.59	8.249%	$200.8993	$200.90	$200.90	$200.90
Purchase #3	$164.91	12.554%	$185.6128	$185.61	$185.60	$185.60
Purchase #4	$196.93	9.268%	$215.1815	$215.18	$215.20	$215.20
Purchase #5	$175.92	13.473%	$199.6217	$199.62	$199.60	$199.60
Purchase #6	$28.92	9.784%	$31.7495	$31.75	$31.75	$31.70
Purchase #7	$212.80	4.642%	$222.6782	$222.68	$222.70	$222.70
7 purchase totals =	$1,099.92		$1,194.7963	$1,194.79	$1,194.80	$1,194.80