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	$164.62	4.155%	$171.46	$171.46	$171.45	$171.50
Purchase #2	$124.79	13.183%	$141.2411	$141.24	$141.25	$141.20
Purchase #3	$122.52	13.541%	$139.1104	$139.11	$139.10	$139.10
Purchase #4	$19.48	12.504%	$21.9158	$21.92	$21.90	$21.90
Purchase #5	$104.77	7.130%	$112.2401	$112.24	$112.25	$112.20
Purchase #6	$76.67	7.312%	$82.2761	$82.28	$82.30	$82.30
Purchase #7	$200.81	10.794%	$222.4854	$222.49	$222.50	$222.50
7 purchase totals =	$813.66		$890.7289	$890.74	$890.75	$890.70