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	$13.39	3.737%	$13.8904	$13.89	$13.90	$13.90
Purchase #2	$82.34	6.314%	$87.5389	$87.54	$87.55	$87.50
Purchase #3	$218.81	9.428%	$239.4394	$239.44	$239.45	$239.40
Purchase #4	$158.65	3.529%	$164.2488	$164.25	$164.25	$164.20
Purchase #5	$59.92	3.716%	$62.1466	$62.15	$62.15	$62.10
Purchase #6	$142.78	9.439%	$156.257	$156.26	$156.25	$156.30
Purchase #7	$144.75	4.850%	$151.7704	$151.77	$151.75	$151.80
7 purchase totals =	$820.64		$875.2915	$875.30	$875.30	$875.20