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	$127.77	9.494%	$139.9005	$139.90	$139.90	$139.90
Purchase #2	$65.78	10.847%	$72.9152	$72.92	$72.90	$72.90
Purchase #3	$153.66	12.397%	$172.7092	$172.71	$172.70	$172.70
Purchase #4	$182.29	13.298%	$206.5309	$206.53	$206.55	$206.50
Purchase #5	$199.29	10.356%	$219.9285	$219.93	$219.95	$219.90
Purchase #6	$171.96	6.353%	$182.8846	$182.88	$182.90	$182.90
Purchase #7	$32.26	3.409%	$33.3597	$33.36	$33.35	$33.40
7 purchase totals =	$933.01		$1,028.2286	$1,028.23	$1,028.25	$1,028.20