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	$219.27	5.733%	$231.8407	$231.84	$231.85	$231.80
Purchase #2	$38.79	12.172%	$43.5115	$43.51	$43.50	$43.50
Purchase #3	$242.62	8.570%	$263.4125	$263.41	$263.40	$263.40
Purchase #4	$232.82	11.624%	$259.883	$259.88	$259.90	$259.90
Purchase #5	$130.51	6.728%	$139.2907	$139.29	$139.30	$139.30
Purchase #6	$134.26	13.122%	$151.8776	$151.88	$151.90	$151.90
Purchase #7	$92.34	8.367%	$100.0661	$100.07	$100.05	$100.10
7 purchase totals =	$1,090.61		$1,189.8821	$1,189.88	$1,189.90	$1,189.90