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	$215.51	12.470%	$242.3841	$242.38	$242.40	$242.40
Purchase #2	$60.57	6.256%	$64.3593	$64.36	$64.35	$64.40
Purchase #3	$233.35	13.710%	$265.3423	$265.34	$265.35	$265.30
Purchase #4	$196.86	10.386%	$217.3059	$217.31	$217.30	$217.30
Purchase #5	$133.43	13.613%	$151.5938	$151.59	$151.60	$151.60
Purchase #6	$76.83	4.646%	$80.3995	$80.40	$80.40	$80.40
Purchase #7	$47.49	4.377%	$49.5686	$49.57	$49.55	$49.60
7 purchase totals =	$964.04		$1,070.9535	$1,070.95	$1,070.95	$1,071.00