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 $68.48   3.644%   $70.9754   $70.98   $71.00   $71.00  
  Purchase #2 $234.89   11.348%   $261.5453   $261.55   $261.55   $261.50  
  Purchase #3 $20.89   13.515%   $23.7133   $23.71   $23.70   $23.70  
  Purchase #4 $152.73   11.393%   $170.1305   $170.13   $170.15   $170.10  
  Purchase #5 $70.46   13.292%   $79.8255   $79.83   $79.85   $79.80  
  Purchase #6 $53.73   4.427%   $56.1086   $56.11   $56.10   $56.10  
  Purchase #7 $235.81   13.637%   $267.9674   $267.97   $267.95   $268.00  
  7 purchase totals = $836.99       $930.2660   $930.28   $930.30   $930.20