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	$30.77	9.652%	$33.7399	$33.74	$33.75	$33.70
Purchase #2	$53.96	6.561%	$57.5003	$57.50	$57.50	$57.50
Purchase #3	$227.84	11.842%	$254.8208	$254.82	$254.80	$254.80
Purchase #4	$201.34	13.472%	$228.4645	$228.46	$228.45	$228.50
Purchase #5	$133.25	11.665%	$148.7936	$148.79	$148.80	$148.80
Purchase #6	$126.52	11.693%	$141.314	$141.31	$141.30	$141.30
Purchase #7	$214.96	7.646%	$231.3958	$231.40	$231.40	$231.40
7 purchase totals =	$988.64		$1,096.0289	$1,096.02	$1,096.00	$1,096.00