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	$208.61	13.440%	$236.6472	$236.65	$236.65	$236.60
Purchase #2	$108.82	13.651%	$123.675	$123.68	$123.70	$123.70
Purchase #3	$88.72	9.614%	$97.2495	$97.25	$97.25	$97.20
Purchase #4	$30.47	4.801%	$31.9329	$31.93	$31.95	$31.90
Purchase #5	$52.91	12.703%	$59.6312	$59.63	$59.65	$59.60
Purchase #6	$90.86	9.696%	$99.6698	$99.67	$99.65	$99.70
Purchase #7	$17.85	9.342%	$19.5175	$19.52	$19.50	$19.50
7 purchase totals =	$598.24		$668.3231	$668.33	$668.35	$668.20