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 $56.98   3.511%   $58.9806   $58.98   $59.00   $59.00  
  Purchase #2 $177.81   4.737%   $186.2329   $186.23   $186.25   $186.20  
  Purchase #3 $222.54   8.170%   $240.7215   $240.72   $240.70   $240.70  
  Purchase #4 $141.77   12.777%   $159.884   $159.88   $159.90   $159.90  
  Purchase #5 $62.58   7.267%   $67.1277   $67.13   $67.15   $67.10  
  Purchase #6 $169.64   13.867%   $193.164   $193.16   $193.15   $193.20  
  Purchase #7 $155.37   9.338%   $169.8785   $169.88   $169.90   $169.90  
  7 purchase totals = $986.69       $1,075.9892   $1,075.98   $1,076.05   $1,076.00