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 $246.30   8.672%   $267.6591   $267.66   $267.65   $267.70  
  Purchase #2 $59.59   6.326%   $63.3597   $63.36   $63.35   $63.40  
  Purchase #3 $62.87   6.402%   $66.8949   $66.89   $66.90   $66.90  
  Purchase #4 $205.84   9.682%   $225.7694   $225.77   $225.75   $225.80  
  Purchase #5 $82.38   9.799%   $90.4524   $90.45   $90.45   $90.50  
  Purchase #6 $228.80   13.638%   $260.0037   $260.00   $260.00   $260.00  
  Purchase #7 $127.86   10.723%   $141.5704   $141.57   $141.55   $141.60  
  7 purchase totals = $1,013.64       $1,115.7096   $1,115.70   $1,115.65   $1,115.90