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 $119.27   12.479%   $134.1537   $134.15   $134.15   $134.20  
  Purchase #2 $157.76   7.349%   $169.3538   $169.35   $169.35   $169.40  
  Purchase #3 $41.77   4.554%   $43.6722   $43.67   $43.65   $43.70  
  Purchase #4 $149.43   10.727%   $165.4594   $165.46   $165.45   $165.50  
  Purchase #5 $7.65   6.588%   $8.154   $8.15   $8.15   $8.20  
  Purchase #6 $71.98   9.501%   $78.8188   $78.82   $78.80   $78.80  
  Purchase #7 $250.39   6.701%   $267.1686   $267.17   $267.15   $267.20  
  7 purchase totals = $798.25       $866.7805   $866.77   $866.70   $867.00