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 $59.54   9.485%   $65.1874   $65.19   $65.20   $65.20  
  Purchase #2 $124.46   10.544%   $137.5831   $137.58   $137.60   $137.60  
  Purchase #3 $73.90   3.435%   $76.4385   $76.44   $76.45   $76.40  
  Purchase #4 $240.69   3.824%   $249.894   $249.89   $249.90   $249.90  
  Purchase #5 $106.45   9.566%   $116.633   $116.63   $116.65   $116.60  
  Purchase #6 $25.83   13.775%   $29.3881   $29.39   $29.40   $29.40  
  Purchase #7 $17.42   7.176%   $18.6701   $18.67   $18.65   $18.70  
  7 purchase totals = $648.29       $693.7942   $693.79   $693.85   $693.80