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 $227.63   11.402%   $253.5844   $253.58   $253.60   $253.60  
  Purchase #2 $182.57   8.289%   $197.7032   $197.70   $197.70   $197.70  
  Purchase #3 $160.39   3.297%   $165.6781   $165.68   $165.70   $165.70  
  Purchase #4 $145.56   7.738%   $156.8234   $156.82   $156.80   $156.80  
  Purchase #5 $70.99   8.173%   $76.792   $76.79   $76.80   $76.80  
  Purchase #6 $234.94   5.498%   $247.857   $247.86   $247.85   $247.90  
  Purchase #7 $228.44   11.329%   $254.32   $254.32   $254.30   $254.30  
  7 purchase totals = $1,250.52       $1,352.7581   $1,352.75   $1,352.75   $1,352.80