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 $245.31   5.652%   $259.1749   $259.17   $259.15   $259.20  
  Purchase #2 $124.29   12.484%   $139.8064   $139.81   $139.80   $139.80  
  Purchase #3 $156.42   8.341%   $169.467   $169.47   $169.45   $169.50  
  Purchase #4 $56.52   13.359%   $64.0705   $64.07   $64.05   $64.10  
  Purchase #5 $115.96   8.112%   $125.3667   $125.37   $125.35   $125.40  
  Purchase #6 $110.75   8.801%   $120.4971   $120.50   $120.50   $120.50  
  Purchase #7 $52.25   8.314%   $56.5941   $56.59   $56.60   $56.60  
  7 purchase totals = $861.50       $934.9767   $934.98   $934.90   $935.10