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	$249.29	4.239%	$259.8574	$259.86	$259.85	$259.90
Purchase #2	$198.44	12.103%	$222.4572	$222.46	$222.45	$222.50
Purchase #3	$110.33	11.492%	$123.0091	$123.01	$123.00	$123.00
Purchase #4	$7.94	8.648%	$8.6267	$8.63	$8.65	$8.60
Purchase #5	$80.61	9.463%	$88.2381	$88.24	$88.25	$88.20
Purchase #6	$71.63	13.313%	$81.1661	$81.17	$81.15	$81.20
Purchase #7	$176.40	10.816%	$195.4794	$195.48	$195.50	$195.50
7 purchase totals =	$894.64		$978.8340	$978.85	$978.85	$978.90