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	$93.49	5.773%	$98.8872	$98.89	$98.90	$98.90
Purchase #2	$57.97	11.189%	$64.4563	$64.46	$64.45	$64.50
Purchase #3	$123.84	11.356%	$137.9033	$137.90	$137.90	$137.90
Purchase #4	$164.84	5.841%	$174.4683	$174.47	$174.45	$174.50
Purchase #5	$81.41	6.736%	$86.8938	$86.89	$86.90	$86.90
Purchase #6	$171.91	8.540%	$186.5911	$186.59	$186.60	$186.60
Purchase #7	$218.56	12.843%	$246.6297	$246.63	$246.65	$246.60
7 purchase totals =	$912.02		$995.8297	$995.83	$995.85	$995.90