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	$159.81	13.440%	$181.2885	$181.29	$181.30	$181.30
Purchase #2	$40.63	6.159%	$43.1324	$43.13	$43.15	$43.10
Purchase #3	$50.57	5.812%	$53.5091	$53.51	$53.50	$53.50
Purchase #4	$60.37	12.686%	$68.0285	$68.03	$68.05	$68.00
Purchase #5	$80.70	12.611%	$90.8771	$90.88	$90.90	$90.90
Purchase #6	$31.39	12.836%	$35.4192	$35.42	$35.40	$35.40
Purchase #7	$61.92	9.214%	$67.6253	$67.63	$67.65	$67.60
7 purchase totals =	$485.39		$539.8801	$539.89	$539.95	$539.80