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 $87.90   6.655%   $93.7497   $93.75   $93.75   $93.70  
  Purchase #2 $55.36   11.421%   $61.6827   $61.68   $61.70   $61.70  
  Purchase #3 $217.87   12.529%   $245.1669   $245.17   $245.15   $245.20  
  Purchase #4 $58.84   11.852%   $65.8137   $65.81   $65.80   $65.80  
  Purchase #5 $236.95   3.796%   $245.9446   $245.94   $245.95   $245.90  
  Purchase #6 $63.98   4.716%   $66.9973   $67.00   $67.00   $67.00  
  Purchase #7 $82.76   5.772%   $87.5369   $87.54   $87.55   $87.50  
  7 purchase totals = $803.66       $866.8918   $866.89   $866.90   $866.80