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 $58.39   5.313%   $61.4923   $61.49   $61.50   $61.50  
  Purchase #2 $190.56   12.135%   $213.6845   $213.68   $213.70   $213.70  
  Purchase #3 $67.63   7.140%   $72.4588   $72.46   $72.45   $72.50  
  Purchase #4 $165.31   8.432%   $179.2489   $179.25   $179.25   $179.20  
  Purchase #5 $76.96   9.425%   $84.2135   $84.21   $84.20   $84.20  
  Purchase #6 $146.85   5.146%   $154.4069   $154.41   $154.40   $154.40  
  Purchase #7 $132.91   6.463%   $141.5   $141.50   $141.50   $141.50  
  7 purchase totals = $838.61       $907.0049   $907.00   $907.00   $907.00