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	$225.40	13.273%	$255.3173	$255.32	$255.30	$255.30
Purchase #2	$55.73	7.557%	$59.9415	$59.94	$59.95	$59.90
Purchase #3	$240.83	11.825%	$269.3081	$269.31	$269.30	$269.30
Purchase #4	$174.61	3.502%	$180.7248	$180.72	$180.70	$180.70
Purchase #5	$40.51	5.645%	$42.7968	$42.80	$42.80	$42.80
Purchase #6	$15.47	8.548%	$16.7924	$16.79	$16.80	$16.80
Purchase #7	$86.86	4.236%	$90.5394	$90.54	$90.55	$90.50
7 purchase totals =	$839.41		$915.4203	$915.42	$915.40	$915.30