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	$55.43	12.703%	$62.4713	$62.47	$62.45	$62.50
Purchase #2	$174.39	8.844%	$189.8131	$189.81	$189.80	$189.80
Purchase #3	$98.41	5.305%	$103.6307	$103.63	$103.65	$103.60
Purchase #4	$104.46	10.329%	$115.2497	$115.25	$115.25	$115.20
Purchase #5	$118.48	4.102%	$123.34	$123.34	$123.35	$123.30
Purchase #6	$18.68	11.850%	$20.8936	$20.89	$20.90	$20.90
Purchase #7	$184.46	8.212%	$199.6079	$199.61	$199.60	$199.60
7 purchase totals =	$754.31		$815.0063	$815.00	$815.00	$814.90