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	$229.55	8.861%	$249.8904	$249.89	$249.90	$249.90
Purchase #2	$152.50	12.270%	$171.2118	$171.21	$171.20	$171.20
Purchase #3	$214.78	11.266%	$238.9771	$238.98	$239.00	$239.00
Purchase #4	$112.38	13.310%	$127.3378	$127.34	$127.35	$127.30
Purchase #5	$227.39	13.849%	$258.8812	$258.88	$258.90	$258.90
Purchase #6	$177.72	4.364%	$185.4757	$185.48	$185.50	$185.50
Purchase #7	$27.29	6.508%	$29.066	$29.07	$29.05	$29.10
7 purchase totals =	$1,141.61		$1,260.8400	$1,260.85	$1,260.90	$1,260.90