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	$90.98	12.401%	$102.2624	$102.26	$102.25	$102.30
Purchase #2	$153.98	6.847%	$164.523	$164.52	$164.50	$164.50
Purchase #3	$231.31	11.312%	$257.4758	$257.48	$257.50	$257.50
Purchase #4	$136.28	10.436%	$150.5022	$150.50	$150.50	$150.50
Purchase #5	$75.60	9.582%	$82.844	$82.84	$82.85	$82.80
Purchase #6	$156.49	9.583%	$171.4864	$171.49	$171.50	$171.50
Purchase #7	$102.76	7.820%	$110.7958	$110.80	$110.80	$110.80
7 purchase totals =	$947.40		$1,039.8896	$1,039.89	$1,039.90	$1,039.90