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	$226.46	6.598%	$241.4018	$241.40	$241.40	$241.40
Purchase #2	$37.64	11.350%	$41.9121	$41.91	$41.90	$41.90
Purchase #3	$209.98	10.238%	$231.4778	$231.48	$231.50	$231.50
Purchase #4	$14.61	5.188%	$15.368	$15.37	$15.35	$15.40
Purchase #5	$169.52	7.501%	$182.2357	$182.24	$182.25	$182.20
Purchase #6	$84.94	6.239%	$90.2394	$90.24	$90.25	$90.20
Purchase #7	$19.59	3.487%	$20.2731	$20.27	$20.25	$20.30
7 purchase totals =	$762.74		$822.9079	$822.91	$822.90	$822.90