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	$108.48	13.846%	$123.5001	$123.50	$123.50	$123.50
Purchase #2	$164.57	10.211%	$181.3742	$181.37	$181.35	$181.40
Purchase #3	$240.58	7.480%	$258.5754	$258.58	$258.60	$258.60
Purchase #4	$176.30	5.820%	$186.5607	$186.56	$186.55	$186.60
Purchase #5	$85.48	11.206%	$95.0589	$95.06	$95.05	$95.10
Purchase #6	$48.91	10.204%	$53.9008	$53.90	$53.90	$53.90
Purchase #7	$215.96	7.386%	$231.9108	$231.91	$231.90	$231.90
7 purchase totals =	$1,040.28		$1,130.8809	$1,130.88	$1,130.85	$1,131.00