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	$15.89	6.602%	$16.9391	$16.94	$16.95	$16.90
Purchase #2	$40.39	4.569%	$42.2354	$42.24	$42.25	$42.20
Purchase #3	$37.54	12.596%	$42.2685	$42.27	$42.25	$42.30
Purchase #4	$39.96	3.156%	$41.2211	$41.22	$41.20	$41.20
Purchase #5	$194.42	12.427%	$218.5806	$218.58	$218.60	$218.60
Purchase #6	$138.86	12.655%	$156.4327	$156.43	$156.45	$156.40
Purchase #7	$130.32	7.360%	$139.9116	$139.91	$139.90	$139.90
7 purchase totals =	$597.38		$657.5890	$657.59	$657.60	$657.50