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	$127.86	7.797%	$137.8292	$137.83	$137.85	$137.80
Purchase #2	$205.27	9.761%	$225.3064	$225.31	$225.30	$225.30
Purchase #3	$208.98	10.587%	$231.1047	$231.10	$231.10	$231.10
Purchase #4	$167.71	3.260%	$173.1773	$173.18	$173.20	$173.20
Purchase #5	$248.40	5.487%	$262.0297	$262.03	$262.05	$262.00
Purchase #6	$27.59	13.503%	$31.3155	$31.32	$31.30	$31.30
Purchase #7	$179.57	11.628%	$200.4504	$200.45	$200.45	$200.50
7 purchase totals =	$1,165.38		$1,261.2132	$1,261.22	$1,261.25	$1,261.20