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 $248.46   5.371%   $261.8048   $261.80   $261.80   $261.80  
  Purchase #2 $30.57   13.176%   $34.5979   $34.60   $34.60   $34.60  
  Purchase #3 $157.64   6.392%   $167.7163   $167.72   $167.70   $167.70  
  Purchase #4 $183.83   11.814%   $205.5477   $205.55   $205.55   $205.50  
  Purchase #5 $29.81   10.441%   $32.9225   $32.92   $32.90   $32.90  
  Purchase #6 $219.71   10.434%   $242.6345   $242.63   $242.65   $242.60  
  Purchase #7 $5.47   8.122%   $5.9143   $5.91   $5.90   $5.90  
  7 purchase totals = $875.49       $951.1380   $951.13   $951.10   $951.00