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	$29.79	12.339%	$33.4658	$33.47	$33.45	$33.50
Purchase #2	$190.80	12.818%	$215.2567	$215.26	$215.25	$215.30
Purchase #3	$175.40	5.633%	$185.2803	$185.28	$185.30	$185.30
Purchase #4	$82.48	12.116%	$92.4733	$92.47	$92.45	$92.50
Purchase #5	$241.69	8.229%	$261.5787	$261.58	$261.60	$261.60
Purchase #6	$101.47	11.302%	$112.9381	$112.94	$112.95	$112.90
Purchase #7	$136.75	3.121%	$141.018	$141.02	$141.00	$141.00
7 purchase totals =	$958.38		$1,042.0109	$1,042.02	$1,042.00	$1,042.10