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 $155.71   13.503%   $176.7355   $176.74   $176.75   $176.70  
  Purchase #2 $149.79   13.248%   $169.6342   $169.63   $169.65   $169.60  
  Purchase #3 $107.46   13.576%   $122.0488   $122.05   $122.05   $122.00  
  Purchase #4 $111.59   6.581%   $118.9337   $118.93   $118.95   $118.90  
  Purchase #5 $36.51   6.179%   $38.766   $38.77   $38.75   $38.80  
  Purchase #6 $205.31   5.281%   $216.1524   $216.15   $216.15   $216.20  
  Purchase #7 $136.34   12.555%   $153.4575   $153.46   $153.45   $153.50  
  7 purchase totals = $902.71       $995.7281   $995.73   $995.75   $995.70