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	$199.90	12.495%	$224.8775	$224.88	$224.90	$224.90
Purchase #2	$205.71	8.351%	$222.8888	$222.89	$222.90	$222.90
Purchase #3	$172.48	9.524%	$188.907	$188.91	$188.90	$188.90
Purchase #4	$137.86	8.870%	$150.0882	$150.09	$150.10	$150.10
Purchase #5	$136.27	3.561%	$141.1226	$141.12	$141.10	$141.10
Purchase #6	$13.98	3.352%	$14.4486	$14.45	$14.45	$14.40
Purchase #7	$32.38	9.868%	$35.5753	$35.58	$35.60	$35.60
7 purchase totals =	$898.58		$977.9080	$977.92	$977.95	$977.90