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 $150.27   9.632%   $164.744   $164.74   $164.75   $164.70  
  Purchase #2 $155.45   6.407%   $165.4097   $165.41   $165.40   $165.40  
  Purchase #3 $116.66   7.448%   $125.3488   $125.35   $125.35   $125.30  
  Purchase #4 $157.61   7.626%   $169.6293   $169.63   $169.65   $169.60  
  Purchase #5 $186.63   8.172%   $201.8814   $201.88   $201.90   $201.90  
  Purchase #6 $67.38   13.723%   $76.6266   $76.63   $76.65   $76.60  
  Purchase #7 $32.75   11.153%   $36.4026   $36.40   $36.40   $36.40  
  7 purchase totals = $866.75       $940.0424   $940.04   $940.10   $939.90