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 $169.75   8.151%   $183.5863   $183.59   $183.60   $183.60  
  Purchase #2 $220.34   9.628%   $241.5543   $241.55   $241.55   $241.60  
  Purchase #3 $32.90   8.535%   $35.708   $35.71   $35.70   $35.70  
  Purchase #4 $241.49   8.459%   $261.9176   $261.92   $261.90   $261.90  
  Purchase #5 $149.99   4.173%   $156.2491   $156.25   $156.25   $156.20  
  Purchase #6 $234.56   4.110%   $244.2004   $244.20   $244.20   $244.20  
  Purchase #7 $244.90   4.435%   $255.7613   $255.76   $255.75   $255.80  
  7 purchase totals = $1,293.93       $1,378.9770   $1,378.98   $1,378.95   $1,379.00