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 $233.82   13.207%   $264.7006   $264.70   $264.70   $264.70  
  Purchase #2 $91.76   8.424%   $99.4899   $99.49   $99.50   $99.50  
  Purchase #3 $125.75   8.131%   $135.9747   $135.97   $135.95   $136.00  
  Purchase #4 $87.89   10.846%   $97.4225   $97.42   $97.40   $97.40  
  Purchase #5 $144.89   13.288%   $164.143   $164.14   $164.15   $164.10  
  Purchase #6 $53.52   9.270%   $58.4813   $58.48   $58.50   $58.50  
  Purchase #7 $218.83   9.194%   $238.9492   $238.95   $238.95   $238.90  
  7 purchase totals = $956.46       $1,059.1612   $1,059.15   $1,059.15   $1,059.10