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	$224.58	10.174%	$247.4288	$247.43	$247.45	$247.40
Purchase #2	$19.33	8.581%	$20.9887	$20.99	$21.00	$21.00
Purchase #3	$205.53	8.459%	$222.9158	$222.92	$222.90	$222.90
Purchase #4	$155.31	3.543%	$160.8126	$160.81	$160.80	$160.80
Purchase #5	$196.59	13.334%	$222.8033	$222.80	$222.80	$222.80
Purchase #6	$204.87	12.707%	$230.9028	$230.90	$230.90	$230.90
Purchase #7	$126.33	13.593%	$143.502	$143.50	$143.50	$143.50
7 purchase totals =	$1,132.54		$1,249.3540	$1,249.35	$1,249.35	$1,249.30