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 $179.29   9.717%   $196.7116   $196.71   $196.70   $196.70  
  Purchase #2 $146.46   10.406%   $161.7006   $161.70   $161.70   $161.70  
  Purchase #3 $139.41   12.637%   $157.0272   $157.03   $157.05   $157.00  
  Purchase #4 $44.77   12.291%   $50.2727   $50.27   $50.25   $50.30  
  Purchase #5 $159.71   6.217%   $169.6392   $169.64   $169.65   $169.60  
  Purchase #6 $164.26   8.433%   $178.112   $178.11   $178.10   $178.10  
  Purchase #7 $40.26   13.184%   $45.5679   $45.57   $45.55   $45.60  
  7 purchase totals = $874.16       $959.0312   $959.03   $959.00   $959.00