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	$238.89	7.165%	$256.0065	$256.01	$256.00	$256.00
Purchase #2	$137.92	6.173%	$146.4338	$146.43	$146.45	$146.40
Purchase #3	$37.37	12.154%	$41.9119	$41.91	$41.90	$41.90
Purchase #4	$185.68	7.550%	$199.6988	$199.70	$199.70	$199.70
Purchase #5	$242.59	10.267%	$267.4967	$267.50	$267.50	$267.50
Purchase #6	$74.42	9.750%	$81.676	$81.68	$81.70	$81.70
Purchase #7	$83.51	5.819%	$88.3694	$88.37	$88.35	$88.40
7 purchase totals =	$1,000.38		$1,081.5931	$1,081.60	$1,081.60	$1,081.60