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	$240.56	3.340%	$248.5947	$248.59	$248.60	$248.60
Purchase #2	$205.95	7.855%	$222.1274	$222.13	$222.15	$222.10
Purchase #3	$114.38	7.597%	$123.0694	$123.07	$123.05	$123.10
Purchase #4	$242.80	11.639%	$271.0595	$271.06	$271.05	$271.10
Purchase #5	$13.66	6.838%	$14.5941	$14.59	$14.60	$14.60
Purchase #6	$223.62	12.674%	$251.9616	$251.96	$251.95	$252.00
Purchase #7	$131.48	9.455%	$143.9114	$143.91	$143.90	$143.90
7 purchase totals =	$1,172.45		$1,275.3181	$1,275.31	$1,275.30	$1,275.40