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	$139.77	3.438%	$144.5753	$144.58	$144.60	$144.60
Purchase #2	$85.66	13.150%	$96.9243	$96.92	$96.90	$96.90
Purchase #3	$186.86	6.204%	$198.4528	$198.45	$198.45	$198.50
Purchase #4	$29.73	13.754%	$33.8191	$33.82	$33.80	$33.80
Purchase #5	$195.28	11.139%	$217.0322	$217.03	$217.05	$217.00
Purchase #6	$53.27	10.493%	$58.8596	$58.86	$58.85	$58.90
Purchase #7	$240.50	10.630%	$266.0652	$266.07	$266.05	$266.10
7 purchase totals =	$931.07		$1,015.7285	$1,015.73	$1,015.70	$1,015.80