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	$10.67	8.171%	$11.5418	$11.54	$11.55	$11.50
Purchase #2	$155.71	10.770%	$172.48	$172.48	$172.50	$172.50
Purchase #3	$141.56	7.448%	$152.1034	$152.10	$152.10	$152.10
Purchase #4	$105.91	12.638%	$119.2949	$119.29	$119.30	$119.30
Purchase #5	$210.54	13.710%	$239.405	$239.41	$239.40	$239.40
Purchase #6	$92.85	5.665%	$98.11	$98.11	$98.10	$98.10
Purchase #7	$130.59	13.272%	$147.9219	$147.92	$147.90	$147.90
7 purchase totals =	$847.83		$940.8570	$940.85	$940.85	$940.80