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	$231.50	13.103%	$261.8334	$261.83	$261.85	$261.80
Purchase #2	$173.58	13.272%	$196.6175	$196.62	$196.60	$196.60
Purchase #3	$64.67	13.652%	$73.4987	$73.50	$73.50	$73.50
Purchase #4	$249.78	9.674%	$273.9437	$273.94	$273.95	$273.90
Purchase #5	$230.30	8.773%	$250.5042	$250.50	$250.50	$250.50
Purchase #6	$104.76	8.505%	$113.6698	$113.67	$113.65	$113.70
Purchase #7	$197.28	8.208%	$213.4727	$213.47	$213.45	$213.50
7 purchase totals =	$1,251.87		$1,383.5400	$1,383.53	$1,383.50	$1,383.50