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 $65.86   8.720%   $71.603   $71.60   $71.60   $71.60  
  Purchase #2 $171.72   3.157%   $177.1412   $177.14   $177.15   $177.10  
  Purchase #3 $49.85   5.402%   $52.5429   $52.54   $52.55   $52.50  
  Purchase #4 $59.98   6.527%   $63.8949   $63.89   $63.90   $63.90  
  Purchase #5 $163.45   13.140%   $184.9273   $184.93   $184.95   $184.90  
  Purchase #6 $151.69   8.512%   $164.6019   $164.60   $164.60   $164.60  
  Purchase #7 $200.70   11.732%   $224.2461   $224.25   $224.25   $224.20  
  7 purchase totals = $863.25       $938.9573   $938.95   $939.00   $938.80