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	$231.83	11.849%	$259.2995	$259.30	$259.30	$259.30
Purchase #2	$163.25	3.279%	$168.603	$168.60	$168.60	$168.60
Purchase #3	$239.78	11.279%	$266.8248	$266.82	$266.80	$266.80
Purchase #4	$81.59	8.868%	$88.8254	$88.83	$88.85	$88.80
Purchase #5	$56.47	6.112%	$59.9214	$59.92	$59.90	$59.90
Purchase #6	$78.33	13.318%	$88.762	$88.76	$88.75	$88.80
Purchase #7	$106.54	9.681%	$116.8541	$116.85	$116.85	$116.90
7 purchase totals =	$957.79		$1,049.0902	$1,049.08	$1,049.05	$1,049.10