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	$5.50	9.229%	$6.0076	$6.01	$6.00	$6.00
Purchase #2	$183.50	13.661%	$208.5679	$208.57	$208.55	$208.60
Purchase #3	$56.95	7.483%	$61.2116	$61.21	$61.20	$61.20
Purchase #4	$113.31	4.236%	$118.1098	$118.11	$118.10	$118.10
Purchase #5	$123.67	13.422%	$140.269	$140.27	$140.25	$140.30
Purchase #6	$186.89	10.455%	$206.4293	$206.43	$206.45	$206.40
Purchase #7	$18.54	9.696%	$20.3376	$20.34	$20.35	$20.30
7 purchase totals =	$688.36		$760.9328	$760.94	$760.90	$760.90