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	$167.89	13.337%	$190.2815	$190.28	$190.30	$190.30
Purchase #2	$234.35	10.476%	$258.9005	$258.90	$258.90	$258.90
Purchase #3	$193.50	8.483%	$209.9146	$209.91	$209.90	$209.90
Purchase #4	$180.88	8.544%	$196.3344	$196.33	$196.35	$196.30
Purchase #5	$186.33	9.448%	$203.9345	$203.93	$203.95	$203.90
Purchase #6	$185.89	8.300%	$201.3189	$201.32	$201.30	$201.30
Purchase #7	$38.78	13.203%	$43.9001	$43.90	$43.90	$43.90
7 purchase totals =	$1,187.62		$1,304.5845	$1,304.57	$1,304.60	$1,304.50