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	$116.73	12.633%	$131.4765	$131.48	$131.50	$131.50
Purchase #2	$83.32	10.466%	$92.0403	$92.04	$92.05	$92.00
Purchase #3	$196.90	8.832%	$214.2902	$214.29	$214.30	$214.30
Purchase #4	$10.69	12.456%	$12.0215	$12.02	$12.00	$12.00
Purchase #5	$178.85	5.869%	$189.3467	$189.35	$189.35	$189.30
Purchase #6	$236.64	9.666%	$259.5136	$259.51	$259.50	$259.50
Purchase #7	$127.69	12.648%	$143.8402	$143.84	$143.85	$143.80
7 purchase totals =	$950.82		$1,042.5290	$1,042.53	$1,042.55	$1,042.40