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 $232.40   12.632%   $261.7568   $261.76   $261.75   $261.80  
  Purchase #2 $174.72   3.507%   $180.8474   $180.85   $180.85   $180.80  
  Purchase #3 $137.66   9.569%   $150.8327   $150.83   $150.85   $150.80  
  Purchase #4 $144.44   12.122%   $161.949   $161.95   $161.95   $161.90  
  Purchase #5 $148.45   4.594%   $155.2698   $155.27   $155.25   $155.30  
  Purchase #6 $199.35   9.619%   $218.5255   $218.53   $218.55   $218.50  
  Purchase #7 $94.44   12.301%   $106.0571   $106.06   $106.05   $106.10  
  7 purchase totals = $1,131.46       $1,235.2383   $1,235.25   $1,235.25   $1,235.20