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	$120.53	8.826%	$131.168	$131.17	$131.15	$131.20
Purchase #2	$186.30	12.109%	$208.8591	$208.86	$208.85	$208.90
Purchase #3	$130.35	8.677%	$141.6605	$141.66	$141.65	$141.70
Purchase #4	$90.36	11.324%	$100.5924	$100.59	$100.60	$100.60
Purchase #5	$88.25	5.771%	$93.3429	$93.34	$93.35	$93.30
Purchase #6	$243.94	9.609%	$267.3802	$267.38	$267.40	$267.40
Purchase #7	$180.30	11.630%	$201.2689	$201.27	$201.25	$201.30
7 purchase totals =	$1,040.03		$1,144.2720	$1,144.27	$1,144.25	$1,144.40