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	$249.95	4.210%	$260.4729	$260.47	$260.45	$260.50
Purchase #2	$91.53	13.556%	$103.9378	$103.94	$103.95	$103.90
Purchase #3	$102.31	9.830%	$112.3671	$112.37	$112.35	$112.40
Purchase #4	$63.63	6.627%	$67.8468	$67.85	$67.85	$67.80
Purchase #5	$117.55	12.240%	$131.9381	$131.94	$131.95	$131.90
Purchase #6	$167.26	11.460%	$186.428	$186.43	$186.45	$186.40
Purchase #7	$140.66	10.862%	$155.9385	$155.94	$155.95	$155.90
7 purchase totals =	$932.89		$1,018.9292	$1,018.94	$1,018.95	$1,018.80