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 $130.83   7.462%   $140.5925   $140.59   $140.60   $140.60  
  Purchase #2 $164.33   6.295%   $174.6746   $174.67   $174.65   $174.70  
  Purchase #3 $114.29   10.537%   $126.3327   $126.33   $126.35   $126.30  
  Purchase #4 $219.66   10.193%   $242.0499   $242.05   $242.05   $242.00  
  Purchase #5 $50.51   11.413%   $56.2747   $56.27   $56.25   $56.30  
  Purchase #6 $169.77   5.262%   $178.7033   $178.70   $178.70   $178.70  
  Purchase #7 $45.77   6.732%   $48.8512   $48.85   $48.85   $48.90  
  7 purchase totals = $895.16       $967.4789   $967.46   $967.45   $967.50