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	$234.88	5.800%	$248.503	$248.50	$248.50	$248.50
Purchase #2	$65.64	8.719%	$71.3632	$71.36	$71.35	$71.40
Purchase #3	$190.70	12.664%	$214.8502	$214.85	$214.85	$214.90
Purchase #4	$44.56	13.440%	$50.5489	$50.55	$50.55	$50.50
Purchase #5	$162.93	4.864%	$170.8549	$170.85	$170.85	$170.90
Purchase #6	$134.36	8.833%	$146.228	$146.23	$146.25	$146.20
Purchase #7	$78.87	12.853%	$89.0072	$89.01	$89.00	$89.00
7 purchase totals =	$911.94		$991.3554	$991.35	$991.35	$991.40