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	$37.93	5.499%	$40.0158	$40.02	$40.00	$40.00
Purchase #2	$83.58	3.441%	$86.456	$86.46	$86.45	$86.50
Purchase #3	$196.72	4.504%	$205.5803	$205.58	$205.60	$205.60
Purchase #4	$168.61	3.157%	$173.933	$173.93	$173.95	$173.90
Purchase #5	$52.70	12.466%	$59.2696	$59.27	$59.25	$59.30
Purchase #6	$241.33	8.154%	$261.008	$261.01	$261.00	$261.00
Purchase #7	$209.92	11.565%	$234.1972	$234.20	$234.20	$234.20
7 purchase totals =	$990.79		$1,060.4599	$1,060.47	$1,060.45	$1,060.50