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	$27.61	12.335%	$31.0157	$31.02	$31.00	$31.00
Purchase #2	$57.27	4.625%	$59.9187	$59.92	$59.90	$59.90
Purchase #3	$229.39	4.704%	$240.1805	$240.18	$240.20	$240.20
Purchase #4	$131.94	5.638%	$139.3788	$139.38	$139.40	$139.40
Purchase #5	$94.45	8.439%	$102.4206	$102.42	$102.40	$102.40
Purchase #6	$131.92	6.577%	$140.5964	$140.60	$140.60	$140.60
Purchase #7	$239.29	3.548%	$247.78	$247.78	$247.80	$247.80
7 purchase totals =	$911.87		$961.2907	$961.30	$961.30	$961.30