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	$17.59	5.853%	$18.6195	$18.62	$18.60	$18.60
Purchase #2	$45.55	13.442%	$51.6728	$51.67	$51.65	$51.70
Purchase #3	$125.71	3.329%	$129.8949	$129.89	$129.90	$129.90
Purchase #4	$185.67	10.751%	$205.6314	$205.63	$205.65	$205.60
Purchase #5	$54.28	10.285%	$59.8627	$59.86	$59.85	$59.90
Purchase #6	$129.48	9.600%	$141.9101	$141.91	$141.90	$141.90
Purchase #7	$171.70	6.166%	$182.287	$182.29	$182.30	$182.30
7 purchase totals =	$729.98		$789.8784	$789.87	$789.85	$789.90