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	$225.78	13.639%	$256.5741	$256.57	$256.55	$256.60
Purchase #2	$248.76	6.104%	$263.9443	$263.94	$263.95	$263.90
Purchase #3	$27.61	13.212%	$31.2578	$31.26	$31.25	$31.30
Purchase #4	$152.42	9.554%	$166.9822	$166.98	$167.00	$167.00
Purchase #5	$31.35	10.181%	$34.5417	$34.54	$34.55	$34.50
Purchase #6	$217.31	12.870%	$245.2778	$245.28	$245.30	$245.30
Purchase #7	$90.39	11.692%	$100.9584	$100.96	$100.95	$101.00
7 purchase totals =	$993.62		$1,099.5363	$1,099.53	$1,099.55	$1,099.60