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 $58.83   8.861%   $64.0429   $64.04   $64.05   $64.00  
  Purchase #2 $156.55   7.247%   $167.8952   $167.90   $167.90   $167.90  
  Purchase #3 $185.50   11.414%   $206.673   $206.67   $206.65   $206.70  
  Purchase #4 $68.82   8.827%   $74.8947   $74.89   $74.90   $74.90  
  Purchase #5 $182.30   3.499%   $188.6787   $188.68   $188.70   $188.70  
  Purchase #6 $197.38   4.781%   $206.8167   $206.82   $206.80   $206.80  
  Purchase #7 $27.60   3.493%   $28.5641   $28.56   $28.55   $28.60  
  7 purchase totals = $876.98       $937.5653   $937.56   $937.55   $937.60