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 $22.76   12.388%   $25.5795   $25.58   $25.60   $25.60  
  Purchase #2 $105.72   7.843%   $114.0116   $114.01   $114.00   $114.00  
  Purchase #3 $25.93   6.712%   $27.6704   $27.67   $27.65   $27.70  
  Purchase #4 $194.44   5.661%   $205.4472   $205.45   $205.45   $205.40  
  Purchase #5 $203.81   12.179%   $228.632   $228.63   $228.65   $228.60  
  Purchase #6 $238.58   5.778%   $252.3652   $252.37   $252.35   $252.40  
  Purchase #7 $25.75   8.539%   $27.9488   $27.95   $27.95   $27.90  
  7 purchase totals = $816.99       $881.6547   $881.66   $881.65   $881.60