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 $84.82   4.798%   $88.8897   $88.89   $88.90   $88.90  
  Purchase #2 $132.62   9.287%   $144.9364   $144.94   $144.95   $144.90  
  Purchase #3 $161.61   8.649%   $175.5876   $175.59   $175.60   $175.60  
  Purchase #4 $184.59   11.167%   $205.2032   $205.20   $205.20   $205.20  
  Purchase #5 $148.61   4.262%   $154.9438   $154.94   $154.95   $154.90  
  Purchase #6 $228.30   5.766%   $241.4638   $241.46   $241.45   $241.50  
  Purchase #7 $23.86   11.649%   $26.6395   $26.64   $26.65   $26.60  
  7 purchase totals = $964.41       $1,037.6640   $1,037.66   $1,037.70   $1,037.60