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	$82.55	5.852%	$87.3808	$87.38	$87.40	$87.40
Purchase #2	$86.58	3.853%	$89.9159	$89.92	$89.90	$89.90
Purchase #3	$218.70	5.571%	$230.8838	$230.88	$230.90	$230.90
Purchase #4	$198.68	7.452%	$213.4856	$213.49	$213.50	$213.50
Purchase #5	$37.76	6.836%	$40.3413	$40.34	$40.35	$40.30
Purchase #6	$42.36	8.340%	$45.8928	$45.89	$45.90	$45.90
Purchase #7	$59.43	6.466%	$63.2727	$63.27	$63.25	$63.30
7 purchase totals =	$726.06		$771.1729	$771.17	$771.20	$771.20