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	$23.38	13.231%	$26.4734	$26.47	$26.45	$26.50
Purchase #2	$86.82	5.521%	$91.6133	$91.61	$91.60	$91.60
Purchase #3	$234.30	11.157%	$260.4409	$260.44	$260.45	$260.40
Purchase #4	$155.93	10.317%	$172.0173	$172.02	$172.00	$172.00
Purchase #5	$36.30	10.213%	$40.0073	$40.01	$40.00	$40.00
Purchase #6	$58.83	6.256%	$62.5104	$62.51	$62.50	$62.50
Purchase #7	$93.79	3.291%	$96.8766	$96.88	$96.90	$96.90
7 purchase totals =	$689.35		$749.9392	$749.94	$749.90	$749.90