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	$128.77	8.651%	$139.9099	$139.91	$139.90	$139.90
Purchase #2	$215.38	12.781%	$242.9077	$242.91	$242.90	$242.90
Purchase #3	$117.25	8.302%	$126.9841	$126.98	$127.00	$127.00
Purchase #4	$169.98	10.378%	$187.6205	$187.62	$187.60	$187.60
Purchase #5	$163.79	12.107%	$183.6201	$183.62	$183.60	$183.60
Purchase #6	$163.43	3.639%	$169.3772	$169.38	$169.40	$169.40
Purchase #7	$65.91	10.676%	$72.9466	$72.95	$72.95	$72.90
7 purchase totals =	$1,024.51		$1,123.3661	$1,123.37	$1,123.35	$1,123.30