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	$141.39	11.554%	$157.7262	$157.73	$157.75	$157.70
Purchase #2	$212.30	4.630%	$222.1295	$222.13	$222.15	$222.10
Purchase #3	$81.81	11.450%	$91.1772	$91.18	$91.20	$91.20
Purchase #4	$191.90	7.656%	$206.5919	$206.59	$206.60	$206.60
Purchase #5	$30.93	4.181%	$32.2232	$32.22	$32.20	$32.20
Purchase #6	$131.44	4.678%	$137.5888	$137.59	$137.60	$137.60
Purchase #7	$128.48	3.398%	$132.8458	$132.85	$132.85	$132.80
7 purchase totals =	$918.25		$980.2826	$980.29	$980.35	$980.20