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	$37.92	11.743%	$42.3729	$42.37	$42.35	$42.40
Purchase #2	$181.55	7.184%	$194.5926	$194.59	$194.60	$194.60
Purchase #3	$123.82	6.328%	$131.6553	$131.66	$131.65	$131.70
Purchase #4	$63.70	4.125%	$66.3276	$66.33	$66.35	$66.30
Purchase #5	$58.84	12.421%	$66.1485	$66.15	$66.15	$66.10
Purchase #6	$84.71	6.854%	$90.516	$90.52	$90.50	$90.50
Purchase #7	$83.38	8.648%	$90.5907	$90.59	$90.60	$90.60
7 purchase totals =	$633.92		$682.2036	$682.21	$682.20	$682.20