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	$106.78	12.452%	$120.0762	$120.08	$120.10	$120.10
Purchase #2	$178.97	3.672%	$185.5418	$185.54	$185.55	$185.50
Purchase #3	$202.48	13.485%	$229.7844	$229.78	$229.80	$229.80
Purchase #4	$11.95	5.544%	$12.6125	$12.61	$12.60	$12.60
Purchase #5	$78.71	8.288%	$85.2335	$85.23	$85.25	$85.20
Purchase #6	$28.83	3.357%	$29.7978	$29.80	$29.80	$29.80
Purchase #7	$156.34	7.750%	$168.4564	$168.46	$168.45	$168.50
7 purchase totals =	$764.06		$831.5026	$831.50	$831.55	$831.50