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	$73.90	12.341%	$83.02	$83.02	$83.00	$83.00
Purchase #2	$187.53	4.631%	$196.2145	$196.21	$196.20	$196.20
Purchase #3	$141.96	8.445%	$153.9485	$153.95	$153.95	$153.90
Purchase #4	$81.47	7.579%	$87.6446	$87.64	$87.65	$87.60
Purchase #5	$134.53	11.551%	$150.0696	$150.07	$150.05	$150.10
Purchase #6	$35.50	7.235%	$38.0684	$38.07	$38.05	$38.10
Purchase #7	$62.99	7.293%	$67.5839	$67.58	$67.60	$67.60
7 purchase totals =	$717.88		$776.5495	$776.54	$776.50	$776.50