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	$140.62	10.822%	$155.8379	$155.84	$155.85	$155.80
Purchase #2	$184.65	12.728%	$208.1523	$208.15	$208.15	$208.20
Purchase #3	$198.92	13.527%	$225.8279	$225.83	$225.85	$225.80
Purchase #4	$179.91	4.154%	$187.3835	$187.38	$187.40	$187.40
Purchase #5	$140.86	5.708%	$148.9003	$148.90	$148.90	$148.90
Purchase #6	$62.37	8.481%	$67.6596	$67.66	$67.65	$67.70
Purchase #7	$213.32	9.590%	$233.7774	$233.78	$233.80	$233.80
7 purchase totals =	$1,120.65		$1,227.5389	$1,227.54	$1,227.60	$1,227.60