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	$137.72	4.830%	$144.3719	$144.37	$144.35	$144.40
Purchase #2	$144.40	12.105%	$161.8796	$161.88	$161.90	$161.90
Purchase #3	$90.35	5.602%	$95.4114	$95.41	$95.40	$95.40
Purchase #4	$158.81	5.848%	$168.0972	$168.10	$168.10	$168.10
Purchase #5	$40.33	12.776%	$45.4826	$45.48	$45.50	$45.50
Purchase #6	$232.85	11.265%	$259.0806	$259.08	$259.10	$259.10
Purchase #7	$103.89	9.312%	$113.5642	$113.56	$113.55	$113.60
7 purchase totals =	$908.35		$987.8875	$987.88	$987.90	$988.00