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	$41.66	3.716%	$43.2081	$43.21	$43.20	$43.20
Purchase #2	$110.66	9.256%	$120.9027	$120.90	$120.90	$120.90
Purchase #3	$176.25	10.447%	$194.6628	$194.66	$194.65	$194.70
Purchase #4	$221.39	13.193%	$250.598	$250.60	$250.60	$250.60
Purchase #5	$42.31	8.299%	$45.8213	$45.82	$45.80	$45.80
Purchase #6	$119.33	10.472%	$131.8262	$131.83	$131.85	$131.80
Purchase #7	$188.34	4.396%	$196.6194	$196.62	$196.60	$196.60
7 purchase totals =	$899.94		$983.6385	$983.64	$983.60	$983.60