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 $61.26   7.116%   $65.6193   $65.62   $65.60   $65.60  
  Purchase #2 $93.88   9.669%   $102.9573   $102.96   $102.95   $103.00  
  Purchase #3 $74.47   13.643%   $84.6299   $84.63   $84.65   $84.60  
  Purchase #4 $138.54   4.706%   $145.0597   $145.06   $145.05   $145.10  
  Purchase #5 $44.70   10.595%   $49.436   $49.44   $49.45   $49.40  
  Purchase #6 $93.75   11.600%   $104.625   $104.63   $104.65   $104.60  
  Purchase #7 $62.59   7.287%   $67.1509   $67.15   $67.15   $67.20  
  7 purchase totals = $569.19       $619.4781   $619.49   $619.50   $619.50