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 $53.74   9.707%   $58.9565   $58.96   $58.95   $59.00  
  Purchase #2 $174.76   3.225%   $180.396   $180.40   $180.40   $180.40  
  Purchase #3 $56.73   5.312%   $59.7435   $59.74   $59.75   $59.70  
  Purchase #4 $235.89   10.668%   $261.0547   $261.05   $261.05   $261.10  
  Purchase #5 $57.86   3.780%   $60.0471   $60.05   $60.05   $60.00  
  Purchase #6 $201.98   9.730%   $221.6327   $221.63   $221.65   $221.60  
  Purchase #7 $144.37   5.437%   $152.2194   $152.22   $152.20   $152.20  
  7 purchase totals = $925.33       $994.0499   $994.05   $994.05   $994.00