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	$88.41	13.134%	$100.0218	$100.02	$100.00	$100.00
Purchase #2	$250.96	13.526%	$284.9048	$284.90	$284.90	$284.90
Purchase #3	$134.55	6.202%	$142.8948	$142.89	$142.90	$142.90
Purchase #4	$22.42	3.181%	$23.1332	$23.13	$23.15	$23.10
Purchase #5	$197.57	10.327%	$217.9731	$217.97	$217.95	$218.00
Purchase #6	$228.66	12.860%	$258.0657	$258.07	$258.05	$258.10
Purchase #7	$137.98	4.602%	$144.3298	$144.33	$144.35	$144.30
7 purchase totals =	$1,060.55		$1,171.3232	$1,171.31	$1,171.30	$1,171.30