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 $217.32   11.182%   $241.6207   $241.62   $241.60   $241.60  
  Purchase #2 $78.56   13.759%   $89.3691   $89.37   $89.35   $89.40  
  Purchase #3 $150.83   11.515%   $168.1981   $168.20   $168.20   $168.20  
  Purchase #4 $193.25   3.141%   $199.32   $199.32   $199.30   $199.30  
  Purchase #5 $67.88   8.552%   $73.6851   $73.69   $73.70   $73.70  
  Purchase #6 $196.58   7.427%   $211.18   $211.18   $211.20   $211.20  
  Purchase #7 $84.49   10.502%   $93.3631   $93.36   $93.35   $93.40  
  7 purchase totals = $988.91       $1,076.7361   $1,076.74   $1,076.70   $1,076.80