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	$145.60	9.565%	$159.5266	$159.53	$159.55	$159.50
Purchase #2	$216.28	9.273%	$236.3356	$236.34	$236.35	$236.30
Purchase #3	$185.68	7.802%	$200.1668	$200.17	$200.15	$200.20
Purchase #4	$180.67	3.791%	$187.5192	$187.52	$187.50	$187.50
Purchase #5	$182.93	7.405%	$196.476	$196.48	$196.50	$196.50
Purchase #6	$146.81	10.267%	$161.883	$161.88	$161.90	$161.90
Purchase #7	$122.71	7.508%	$131.9231	$131.92	$131.90	$131.90
7 purchase totals =	$1,180.68		$1,273.8303	$1,273.84	$1,273.85	$1,273.80