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 $184.39   9.319%   $201.5733   $201.57   $201.55   $201.60  
  Purchase #2 $72.37   12.193%   $81.1941   $81.19   $81.20   $81.20  
  Purchase #3 $154.58   12.244%   $173.5068   $173.51   $173.50   $173.50  
  Purchase #4 $250.65   13.273%   $283.9188   $283.92   $283.90   $283.90  
  Purchase #5 $54.41   8.237%   $58.8918   $58.89   $58.90   $58.90  
  Purchase #6 $128.87   6.645%   $137.4334   $137.43   $137.45   $137.40  
  Purchase #7 $26.33   6.511%   $28.0443   $28.04   $28.05   $28.00  
  7 purchase totals = $871.60       $964.5625   $964.55   $964.55   $964.50