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	$248.50	3.752%	$257.8237	$257.82	$257.80	$257.80
Purchase #2	$244.80	10.850%	$271.3608	$271.36	$271.35	$271.40
Purchase #3	$34.36	10.299%	$37.8987	$37.90	$37.90	$37.90
Purchase #4	$24.43	11.738%	$27.2976	$27.30	$27.30	$27.30
Purchase #5	$75.38	4.231%	$78.5693	$78.57	$78.55	$78.60
Purchase #6	$161.35	11.563%	$180.0069	$180.01	$180.00	$180.00
Purchase #7	$212.89	3.561%	$220.471	$220.47	$220.45	$220.50
7 purchase totals =	$1,001.71		$1,073.4280	$1,073.43	$1,073.35	$1,073.50