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 $59.32   11.575%   $66.1863   $66.19   $66.20   $66.20  
  Purchase #2 $181.72   6.457%   $193.4537   $193.45   $193.45   $193.50  
  Purchase #3 $196.65   7.326%   $211.0566   $211.06   $211.05   $211.10  
  Purchase #4 $142.84   8.421%   $154.8686   $154.87   $154.85   $154.90  
  Purchase #5 $156.95   5.709%   $165.9103   $165.91   $165.90   $165.90  
  Purchase #6 $57.84   10.854%   $64.118   $64.12   $64.10   $64.10  
  Purchase #7 $59.77   4.827%   $62.6551   $62.66   $62.65   $62.70  
  7 purchase totals = $855.09       $918.2486   $918.26   $918.20   $918.40