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	$85.82	5.239%	$90.3161	$90.32	$90.30	$90.30
Purchase #2	$168.63	10.170%	$185.7797	$185.78	$185.80	$185.80
Purchase #3	$220.70	7.119%	$236.4116	$236.41	$236.40	$236.40
Purchase #4	$172.35	11.859%	$192.789	$192.79	$192.80	$192.80
Purchase #5	$109.53	11.528%	$122.1566	$122.16	$122.15	$122.20
Purchase #6	$137.46	4.681%	$143.8945	$143.89	$143.90	$143.90
Purchase #7	$24.55	10.640%	$27.1621	$27.16	$27.15	$27.20
7 purchase totals =	$919.04		$998.5096	$998.51	$998.50	$998.60