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	$73.95	12.117%	$82.9105	$82.91	$82.90	$82.90
Purchase #2	$18.58	7.622%	$19.9962	$20.00	$20.00	$20.00
Purchase #3	$123.50	10.541%	$136.5181	$136.52	$136.50	$136.50
Purchase #4	$113.45	3.254%	$117.1417	$117.14	$117.15	$117.10
Purchase #5	$170.89	10.799%	$189.3444	$189.34	$189.35	$189.30
Purchase #6	$137.47	3.531%	$142.3241	$142.32	$142.30	$142.30
Purchase #7	$102.63	9.586%	$112.4681	$112.47	$112.45	$112.50
7 purchase totals =	$740.47		$800.7031	$800.70	$800.65	$800.60