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	$102.56	9.732%	$112.5411	$112.54	$112.55	$112.50
Purchase #2	$214.86	5.455%	$226.5806	$226.58	$226.60	$226.60
Purchase #3	$111.92	10.104%	$123.2284	$123.23	$123.25	$123.20
Purchase #4	$209.29	8.755%	$227.6133	$227.61	$227.60	$227.60
Purchase #5	$94.85	8.299%	$102.7216	$102.72	$102.70	$102.70
Purchase #6	$83.29	7.838%	$89.8183	$89.82	$89.80	$89.80
Purchase #7	$243.88	5.272%	$256.7374	$256.74	$256.75	$256.70
7 purchase totals =	$1,060.65		$1,139.2407	$1,139.24	$1,139.25	$1,139.10