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	$29.48	6.605%	$31.4272	$31.43	$31.45	$31.40
Purchase #2	$109.78	9.575%	$120.2914	$120.29	$120.30	$120.30
Purchase #3	$150.66	13.208%	$170.5592	$170.56	$170.55	$170.60
Purchase #4	$173.82	3.279%	$179.5196	$179.52	$179.50	$179.50
Purchase #5	$130.35	13.789%	$148.324	$148.32	$148.30	$148.30
Purchase #6	$163.38	6.824%	$174.5291	$174.53	$174.55	$174.50
Purchase #7	$162.29	10.684%	$179.6291	$179.63	$179.65	$179.60
7 purchase totals =	$919.76		$1,004.2796	$1,004.28	$1,004.30	$1,004.20