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 $62.48   10.673%   $69.1485   $69.15   $69.15   $69.10  
  Purchase #2 $56.59   3.710%   $58.6895   $58.69   $58.70   $58.70  
  Purchase #3 $90.62   6.661%   $96.6562   $96.66   $96.65   $96.70  
  Purchase #4 $174.81   13.594%   $198.5737   $198.57   $198.55   $198.60  
  Purchase #5 $191.86   6.618%   $204.5573   $204.56   $204.55   $204.60  
  Purchase #6 $155.55   8.326%   $168.5011   $168.50   $168.50   $168.50  
  Purchase #7 $243.45   7.500%   $261.7088   $261.71   $261.70   $261.70  
  7 purchase totals = $975.36       $1,057.8351   $1,057.84   $1,057.80   $1,057.90