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	$34.79	10.595%	$38.476	$38.48	$38.50	$38.50
Purchase #2	$147.61	8.548%	$160.2277	$160.23	$160.25	$160.20
Purchase #3	$113.93	8.799%	$123.9547	$123.95	$123.95	$124.00
Purchase #4	$125.41	4.548%	$131.1136	$131.11	$131.10	$131.10
Purchase #5	$207.66	8.287%	$224.8688	$224.87	$224.85	$224.90
Purchase #6	$230.27	3.398%	$238.0946	$238.09	$238.10	$238.10
Purchase #7	$79.70	8.715%	$86.6459	$86.65	$86.65	$86.60
7 purchase totals =	$939.37		$1,003.3813	$1,003.38	$1,003.40	$1,003.40