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	$236.91	13.388%	$268.6275	$268.63	$268.65	$268.60
Purchase #2	$218.95	4.372%	$228.5225	$228.52	$228.50	$228.50
Purchase #3	$100.34	3.120%	$103.4706	$103.47	$103.45	$103.50
Purchase #4	$156.72	5.245%	$164.94	$164.94	$164.95	$164.90
Purchase #5	$140.69	13.492%	$159.6719	$159.67	$159.65	$159.70
Purchase #6	$66.48	10.166%	$73.2384	$73.24	$73.25	$73.20
Purchase #7	$35.91	5.571%	$37.9105	$37.91	$37.90	$37.90
7 purchase totals =	$956.00		$1,036.3814	$1,036.38	$1,036.35	$1,036.30