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	$208.90	9.354%	$228.4405	$228.44	$228.45	$228.40
Purchase #2	$198.57	10.703%	$219.8229	$219.82	$219.80	$219.80
Purchase #3	$143.47	9.170%	$156.6262	$156.63	$156.65	$156.60
Purchase #4	$162.83	13.295%	$184.4782	$184.48	$184.50	$184.50
Purchase #5	$94.47	6.337%	$100.4566	$100.46	$100.45	$100.50
Purchase #6	$44.43	7.733%	$47.8658	$47.87	$47.85	$47.90
Purchase #7	$233.65	7.215%	$250.5078	$250.51	$250.50	$250.50
7 purchase totals =	$1,086.32		$1,188.1980	$1,188.21	$1,188.20	$1,188.20