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	$207.36	13.554%	$235.4656	$235.47	$235.45	$235.50
Purchase #2	$165.39	10.592%	$182.9081	$182.91	$182.90	$182.90
Purchase #3	$37.40	13.230%	$42.348	$42.35	$42.35	$42.30
Purchase #4	$82.71	5.712%	$87.4344	$87.43	$87.45	$87.40
Purchase #5	$144.27	8.238%	$156.155	$156.16	$156.15	$156.20
Purchase #6	$194.67	7.849%	$209.9496	$209.95	$209.95	$209.90
Purchase #7	$51.30	10.389%	$56.6296	$56.63	$56.65	$56.60
7 purchase totals =	$883.10		$970.8903	$970.90	$970.90	$970.80