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	$122.53	3.468%	$126.7793	$126.78	$126.80	$126.80
Purchase #2	$104.71	11.526%	$116.7789	$116.78	$116.80	$116.80
Purchase #3	$40.56	9.868%	$44.5625	$44.56	$44.55	$44.60
Purchase #4	$80.96	11.742%	$90.4663	$90.47	$90.45	$90.50
Purchase #5	$222.76	8.798%	$242.3584	$242.36	$242.35	$242.40
Purchase #6	$187.90	3.102%	$193.7287	$193.73	$193.75	$193.70
Purchase #7	$109.30	4.164%	$113.8513	$113.85	$113.85	$113.90
7 purchase totals =	$868.72		$928.5254	$928.53	$928.55	$928.70