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	$51.72	11.142%	$57.4826	$57.48	$57.50	$57.50
Purchase #2	$213.71	6.467%	$227.5306	$227.53	$227.55	$227.50
Purchase #3	$38.88	10.870%	$43.1063	$43.11	$43.10	$43.10
Purchase #4	$22.89	7.272%	$24.5546	$24.55	$24.55	$24.60
Purchase #5	$10.72	8.697%	$11.6523	$11.65	$11.65	$11.70
Purchase #6	$91.84	8.604%	$99.7419	$99.74	$99.75	$99.70
Purchase #7	$11.88	11.122%	$13.2013	$13.20	$13.20	$13.20
7 purchase totals =	$441.64		$477.2696	$477.26	$477.30	$477.30