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	$35.38	13.241%	$40.0647	$40.06	$40.05	$40.10
Purchase #2	$44.64	6.464%	$47.5255	$47.53	$47.55	$47.50
Purchase #3	$125.37	9.136%	$136.8238	$136.82	$136.80	$136.80
Purchase #4	$165.61	5.795%	$175.2071	$175.21	$175.20	$175.20
Purchase #5	$14.78	4.811%	$15.4911	$15.49	$15.50	$15.50
Purchase #6	$165.83	10.389%	$183.0581	$183.06	$183.05	$183.10
Purchase #7	$72.86	12.605%	$82.044	$82.04	$82.05	$82.00
7 purchase totals =	$624.47		$680.2143	$680.21	$680.20	$680.20