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	$112.38	10.706%	$124.4114	$124.41	$124.40	$124.40
Purchase #2	$127.58	7.269%	$136.8538	$136.85	$136.85	$136.90
Purchase #3	$123.46	12.473%	$138.8592	$138.86	$138.85	$138.90
Purchase #4	$215.42	4.733%	$225.6158	$225.62	$225.60	$225.60
Purchase #5	$188.64	5.406%	$198.8379	$198.84	$198.85	$198.80
Purchase #6	$24.57	4.663%	$25.7157	$25.72	$25.70	$25.70
Purchase #7	$82.71	8.277%	$89.5559	$89.56	$89.55	$89.60
7 purchase totals =	$874.76		$939.8497	$939.86	$939.80	$939.90