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	$124.27	10.310%	$137.0822	$137.08	$137.10	$137.10
Purchase #2	$25.48	11.387%	$28.3814	$28.38	$28.40	$28.40
Purchase #3	$232.27	9.862%	$255.1765	$255.18	$255.20	$255.20
Purchase #4	$228.43	4.569%	$238.867	$238.87	$238.85	$238.90
Purchase #5	$169.25	10.397%	$186.8469	$186.85	$186.85	$186.80
Purchase #6	$78.34	8.680%	$85.1399	$85.14	$85.15	$85.10
Purchase #7	$112.49	11.551%	$125.4837	$125.48	$125.50	$125.50
7 purchase totals =	$970.53		$1,056.9776	$1,056.98	$1,057.05	$1,057.00