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 $209.63   11.601%   $233.9492   $233.95   $233.95   $233.90  
  Purchase #2 $147.94   12.117%   $165.8659   $165.87   $165.85   $165.90  
  Purchase #3 $241.55   11.249%   $268.722   $268.72   $268.70   $268.70  
  Purchase #4 $93.50   7.771%   $100.7659   $100.77   $100.75   $100.80  
  Purchase #5 $232.95   13.418%   $264.2072   $264.21   $264.20   $264.20  
  Purchase #6 $114.30   7.157%   $122.4805   $122.48   $122.50   $122.50  
  Purchase #7 $161.34   13.764%   $183.5468   $183.55   $183.55   $183.50  
  7 purchase totals = $1,201.21       $1,339.5375   $1,339.55   $1,339.50   $1,339.50