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	$125.53	11.448%	$139.9007	$139.90	$139.90	$139.90
Purchase #2	$48.74	8.709%	$52.9848	$52.98	$53.00	$53.00
Purchase #3	$84.65	10.569%	$93.5967	$93.60	$93.60	$93.60
Purchase #4	$232.58	12.624%	$261.9409	$261.94	$261.95	$261.90
Purchase #5	$209.46	7.842%	$225.8859	$225.89	$225.90	$225.90
Purchase #6	$67.74	7.175%	$72.6003	$72.60	$72.60	$72.60
Purchase #7	$238.70	4.381%	$249.1574	$249.16	$249.15	$249.20
7 purchase totals =	$1,007.40		$1,096.0667	$1,096.07	$1,096.10	$1,096.10