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	$249.37	9.746%	$273.6736	$273.67	$273.65	$273.70
Purchase #2	$84.72	9.447%	$92.7235	$92.72	$92.70	$92.70
Purchase #3	$103.75	7.270%	$111.2926	$111.29	$111.30	$111.30
Purchase #4	$37.66	10.368%	$41.5646	$41.56	$41.55	$41.60
Purchase #5	$124.51	4.622%	$130.2649	$130.26	$130.25	$130.30
Purchase #6	$31.32	8.616%	$34.0185	$34.02	$34.00	$34.00
Purchase #7	$138.36	12.667%	$155.8861	$155.89	$155.90	$155.90
7 purchase totals =	$769.69		$839.4238	$839.41	$839.35	$839.50