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 $85.73   8.414%   $92.9433   $92.94   $92.95   $92.90  
  Purchase #2 $127.26   8.698%   $138.3291   $138.33   $138.35   $138.30  
  Purchase #3 $75.61   10.651%   $83.6632   $83.66   $83.65   $83.70  
  Purchase #4 $164.42   9.403%   $179.8804   $179.88   $179.90   $179.90  
  Purchase #5 $169.68   3.722%   $175.9955   $176.00   $176.00   $176.00  
  Purchase #6 $102.46   10.691%   $113.414   $113.41   $113.40   $113.40  
  Purchase #7 $171.31   3.563%   $177.4138   $177.41   $177.40   $177.40  
  7 purchase totals = $896.47       $961.6393   $961.63   $961.65   $961.60