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	$123.26	6.507%	$131.2805	$131.28	$131.30	$131.30
Purchase #2	$160.31	11.565%	$178.8499	$178.85	$178.85	$178.80
Purchase #3	$222.90	3.416%	$230.5143	$230.51	$230.50	$230.50
Purchase #4	$31.90	12.534%	$35.8983	$35.90	$35.90	$35.90
Purchase #5	$51.76	7.245%	$55.51	$55.51	$55.50	$55.50
Purchase #6	$90.55	13.134%	$102.4428	$102.44	$102.45	$102.40
Purchase #7	$240.59	3.738%	$249.5833	$249.58	$249.60	$249.60
7 purchase totals =	$921.27		$984.0791	$984.07	$984.10	$984.00