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	$38.47	10.332%	$42.4447	$42.44	$42.45	$42.40
Purchase #2	$137.33	7.799%	$148.0404	$148.04	$148.05	$148.00
Purchase #3	$138.32	3.162%	$142.6937	$142.69	$142.70	$142.70
Purchase #4	$31.46	13.599%	$35.7382	$35.74	$35.75	$35.70
Purchase #5	$141.83	9.473%	$155.2656	$155.27	$155.25	$155.30
Purchase #6	$156.31	9.278%	$170.8124	$170.81	$170.80	$170.80
Purchase #7	$128.50	6.176%	$136.4362	$136.44	$136.45	$136.40
7 purchase totals =	$772.22		$831.4312	$831.43	$831.45	$831.30