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	$112.70	9.341%	$123.2273	$123.23	$123.25	$123.20
Purchase #2	$225.28	9.463%	$246.5982	$246.60	$246.60	$246.60
Purchase #3	$136.67	5.151%	$143.7099	$143.71	$143.70	$143.70
Purchase #4	$232.63	5.687%	$245.8597	$245.86	$245.85	$245.90
Purchase #5	$71.34	13.439%	$80.9274	$80.93	$80.95	$80.90
Purchase #6	$45.53	9.542%	$49.8745	$49.87	$49.85	$49.90
Purchase #7	$124.32	5.627%	$131.3155	$131.32	$131.30	$131.30
7 purchase totals =	$948.47		$1,021.5125	$1,021.52	$1,021.50	$1,021.50