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	$228.88	6.373%	$243.4665	$243.47	$243.45	$243.50
Purchase #2	$186.54	6.393%	$198.4655	$198.47	$198.45	$198.50
Purchase #3	$133.89	8.727%	$145.5746	$145.57	$145.55	$145.60
Purchase #4	$88.95	7.102%	$95.2672	$95.27	$95.25	$95.30
Purchase #5	$49.58	12.657%	$55.8553	$55.86	$55.85	$55.90
Purchase #6	$120.43	9.261%	$131.583	$131.58	$131.60	$131.60
Purchase #7	$124.64	11.786%	$139.3301	$139.33	$139.35	$139.30
7 purchase totals =	$932.91		$1,009.5422	$1,009.55	$1,009.50	$1,009.70