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 $58.54   12.138%   $65.6456   $65.65   $65.65   $65.60  
  Purchase #2 $120.28   5.568%   $126.9772   $126.98   $127.00   $127.00  
  Purchase #3 $105.96   6.356%   $112.6948   $112.69   $112.70   $112.70  
  Purchase #4 $179.35   12.669%   $202.0719   $202.07   $202.05   $202.10  
  Purchase #5 $146.51   3.573%   $151.7448   $151.74   $151.75   $151.70  
  Purchase #6 $236.60   10.696%   $261.9067   $261.91   $261.90   $261.90  
  Purchase #7 $122.95   9.808%   $135.0089   $135.01   $135.00   $135.00  
  7 purchase totals = $970.19       $1,056.0499   $1,056.05   $1,056.05   $1,056.00