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	$118.72	5.619%	$125.3909	$125.39	$125.40	$125.40
Purchase #2	$150.97	9.215%	$164.8819	$164.88	$164.90	$164.90
Purchase #3	$202.73	9.221%	$221.4237	$221.42	$221.40	$221.40
Purchase #4	$11.81	5.687%	$12.4816	$12.48	$12.50	$12.50
Purchase #5	$134.32	3.811%	$139.4389	$139.44	$139.45	$139.40
Purchase #6	$139.79	3.141%	$144.1808	$144.18	$144.20	$144.20
Purchase #7	$245.39	13.805%	$279.2661	$279.27	$279.25	$279.30
7 purchase totals =	$1,003.73		$1,087.0639	$1,087.06	$1,087.10	$1,087.10