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 $55.83   11.159%   $62.0601   $62.06   $62.05   $62.10  
  Purchase #2 $26.59   5.820%   $28.1375   $28.14   $28.15   $28.10  
  Purchase #3 $85.97   8.242%   $93.0556   $93.06   $93.05   $93.10  
  Purchase #4 $90.50   3.280%   $93.4684   $93.47   $93.45   $93.50  
  Purchase #5 $132.52   6.153%   $140.674   $140.67   $140.65   $140.70  
  Purchase #6 $125.54   8.281%   $135.936   $135.94   $135.95   $135.90  
  Purchase #7 $218.80   12.666%   $246.5132   $246.51   $246.50   $246.50  
  7 purchase totals = $735.75       $799.8448   $799.85   $799.80   $799.90