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 $136.57   11.817%   $152.7085   $152.71   $152.70   $152.70  
  Purchase #2 $244.75   10.637%   $270.7841   $270.78   $270.80   $270.80  
  Purchase #3 $23.40   5.797%   $24.7565   $24.76   $24.75   $24.80  
  Purchase #4 $232.47   11.301%   $258.7414   $258.74   $258.75   $258.70  
  Purchase #5 $12.27   11.622%   $13.696   $13.70   $13.70   $13.70  
  Purchase #6 $236.30   10.673%   $261.5203   $261.52   $261.50   $261.50  
  Purchase #7 $10.75   11.158%   $11.9495   $11.95   $11.95   $11.90  
  7 purchase totals = $896.51       $994.1563   $994.16   $994.15   $994.10