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	$75.45	13.232%	$85.4335	$85.43	$85.45	$85.40
Purchase #2	$102.83	8.176%	$111.2374	$111.24	$111.25	$111.20
Purchase #3	$77.49	9.696%	$85.0034	$85.00	$85.00	$85.00
Purchase #4	$217.67	7.298%	$233.5556	$233.56	$233.55	$233.60
Purchase #5	$82.92	9.165%	$90.5196	$90.52	$90.50	$90.50
Purchase #6	$176.55	9.263%	$192.9038	$192.90	$192.90	$192.90
Purchase #7	$184.43	5.787%	$195.103	$195.10	$195.10	$195.10
7 purchase totals =	$917.34		$993.7563	$993.75	$993.75	$993.70