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	$12.96	10.499%	$14.3207	$14.32	$14.30	$14.30
Purchase #2	$229.84	8.540%	$249.4683	$249.47	$249.45	$249.50
Purchase #3	$97.54	11.192%	$108.4567	$108.46	$108.45	$108.50
Purchase #4	$39.28	4.167%	$40.9168	$40.92	$40.90	$40.90
Purchase #5	$131.94	9.264%	$144.1629	$144.16	$144.15	$144.20
Purchase #6	$184.84	13.555%	$209.8951	$209.90	$209.90	$209.90
Purchase #7	$75.52	9.255%	$82.5094	$82.51	$82.50	$82.50
7 purchase totals =	$771.92		$849.7299	$849.74	$849.65	$849.80