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	$201.54	3.622%	$208.8398	$208.84	$208.85	$208.80
Purchase #2	$114.30	5.177%	$120.2173	$120.22	$120.20	$120.20
Purchase #3	$185.98	7.159%	$199.2943	$199.29	$199.30	$199.30
Purchase #4	$80.79	10.430%	$89.2164	$89.22	$89.20	$89.20
Purchase #5	$171.59	8.324%	$185.8732	$185.87	$185.85	$185.90
Purchase #6	$230.25	12.266%	$258.4925	$258.49	$258.50	$258.50
Purchase #7	$47.93	9.592%	$52.5274	$52.53	$52.55	$52.50
7 purchase totals =	$1,032.38		$1,114.4609	$1,114.46	$1,114.45	$1,114.40