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	$131.62	9.542%	$144.1792	$144.18	$144.20	$144.20
Purchase #2	$204.28	13.520%	$231.8987	$231.90	$231.90	$231.90
Purchase #3	$210.45	13.712%	$239.3069	$239.31	$239.30	$239.30
Purchase #4	$242.89	7.796%	$261.8257	$261.83	$261.85	$261.80
Purchase #5	$39.48	3.360%	$40.8065	$40.81	$40.80	$40.80
Purchase #6	$56.83	5.152%	$59.7579	$59.76	$59.75	$59.80
Purchase #7	$238.67	11.791%	$266.8116	$266.81	$266.80	$266.80
7 purchase totals =	$1,124.22		$1,244.5865	$1,244.60	$1,244.60	$1,244.60