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	$19.98	9.787%	$21.9354	$21.94	$21.95	$21.90
Purchase #2	$204.48	8.829%	$222.5335	$222.53	$222.55	$222.50
Purchase #3	$155.47	10.446%	$171.7104	$171.71	$171.70	$171.70
Purchase #4	$230.88	3.180%	$238.222	$238.22	$238.20	$238.20
Purchase #5	$133.38	3.294%	$137.7735	$137.77	$137.75	$137.80
Purchase #6	$39.92	9.184%	$43.5863	$43.59	$43.60	$43.60
Purchase #7	$247.67	11.804%	$276.905	$276.91	$276.90	$276.90
7 purchase totals =	$1,031.78		$1,112.6661	$1,112.67	$1,112.65	$1,112.60