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	$57.88	12.110%	$64.8893	$64.89	$64.90	$64.90
Purchase #2	$196.90	13.246%	$222.9814	$222.98	$223.00	$223.00
Purchase #3	$24.91	6.227%	$26.4611	$26.46	$26.45	$26.50
Purchase #4	$150.53	9.779%	$165.2503	$165.25	$165.25	$165.30
Purchase #5	$131.63	7.354%	$141.3101	$141.31	$141.30	$141.30
Purchase #6	$148.85	5.446%	$156.9564	$156.96	$156.95	$157.00
Purchase #7	$177.58	12.630%	$200.0084	$200.01	$200.00	$200.00
7 purchase totals =	$888.28		$977.8570	$977.86	$977.85	$978.00