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	$38.90	6.206%	$41.3141	$41.31	$41.30	$41.30
Purchase #2	$214.47	3.691%	$222.3861	$222.39	$222.40	$222.40
Purchase #3	$172.81	4.593%	$180.7472	$180.75	$180.75	$180.70
Purchase #4	$168.97	10.785%	$187.1934	$187.19	$187.20	$187.20
Purchase #5	$192.79	9.114%	$210.3609	$210.36	$210.35	$210.40
Purchase #6	$48.30	12.527%	$54.3505	$54.35	$54.35	$54.40
Purchase #7	$175.67	5.342%	$185.0543	$185.05	$185.05	$185.10
7 purchase totals =	$1,011.91		$1,081.4065	$1,081.40	$1,081.40	$1,081.50