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 $59.81   13.579%   $67.9316   $67.93   $67.95   $67.90  
  Purchase #2 $63.35   5.234%   $66.6657   $66.67   $66.65   $66.70  
  Purchase #3 $112.41   9.311%   $122.8765   $122.88   $122.90   $122.90  
  Purchase #4 $180.55   13.367%   $204.6841   $204.68   $204.70   $204.70  
  Purchase #5 $31.33   4.727%   $32.811   $32.81   $32.80   $32.80  
  Purchase #6 $226.50   13.858%   $257.8884   $257.89   $257.90   $257.90  
  Purchase #7 $28.86   9.490%   $31.5988   $31.60   $31.60   $31.60  
  7 purchase totals = $702.81       $784.4561   $784.46   $784.50   $784.50