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	$13.59	4.469%	$14.1973	$14.20	$14.20	$14.20
Purchase #2	$37.67	11.869%	$42.1411	$42.14	$42.15	$42.10
Purchase #3	$79.52	11.269%	$88.4811	$88.48	$88.50	$88.50
Purchase #4	$116.81	9.597%	$128.0203	$128.02	$128.00	$128.00
Purchase #5	$250.32	12.709%	$282.1332	$282.13	$282.15	$282.10
Purchase #6	$131.48	9.111%	$143.4591	$143.46	$143.45	$143.50
Purchase #7	$131.88	3.603%	$136.6316	$136.63	$136.65	$136.60
7 purchase totals =	$761.27		$835.0637	$835.06	$835.10	$835.00