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 $212.89   6.738%   $227.2345   $227.23   $227.25   $227.20  
  Purchase #2 $179.87   7.662%   $193.6516   $193.65   $193.65   $193.70  
  Purchase #3 $57.81   5.377%   $60.9184   $60.92   $60.90   $60.90  
  Purchase #4 $248.40   8.575%   $269.7003   $269.70   $269.70   $269.70  
  Purchase #5 $219.92   9.765%   $241.3952   $241.40   $241.40   $241.40  
  Purchase #6 $111.29   13.840%   $126.6925   $126.69   $126.70   $126.70  
  Purchase #7 $202.41   11.133%   $224.9443   $224.94   $224.95   $224.90  
  7 purchase totals = $1,232.59       $1,344.5368   $1,344.53   $1,344.55   $1,344.50