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 $57.41   13.239%   $65.0105   $65.01   $65.00   $65.00  
  Purchase #2 $59.81   8.398%   $64.8328   $64.83   $64.85   $64.80  
  Purchase #3 $126.97   5.261%   $133.6499   $133.65   $133.65   $133.60  
  Purchase #4 $131.82   11.176%   $146.5522   $146.55   $146.55   $146.60  
  Purchase #5 $44.34   8.309%   $48.0242   $48.02   $48.00   $48.00  
  Purchase #6 $242.76   5.469%   $256.0365   $256.04   $256.05   $256.00  
  Purchase #7 $75.56   13.545%   $85.7946   $85.79   $85.80   $85.80  
  7 purchase totals = $738.67       $799.9007   $799.89   $799.90   $799.80