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 $84.67   11.653%   $94.5366   $94.54   $94.55   $94.50  
  Purchase #2 $45.85   12.186%   $51.4373   $51.44   $51.45   $51.40  
  Purchase #3 $228.30   12.710%   $257.3169   $257.32   $257.30   $257.30  
  Purchase #4 $13.58   8.196%   $14.693   $14.69   $14.70   $14.70  
  Purchase #5 $161.40   9.254%   $176.336   $176.34   $176.35   $176.30  
  Purchase #6 $248.47   5.267%   $261.5569   $261.56   $261.55   $261.60  
  Purchase #7 $117.50   10.476%   $129.8093   $129.81   $129.80   $129.80  
  7 purchase totals = $899.77       $985.6860   $985.70   $985.70   $985.60