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 $96.57   8.693%   $104.9648   $104.96   $104.95   $105.00  
  Purchase #2 $125.56   10.626%   $138.902   $138.90   $138.90   $138.90  
  Purchase #3 $84.55   8.126%   $91.4205   $91.42   $91.40   $91.40  
  Purchase #4 $51.27   7.321%   $55.0235   $55.02   $55.00   $55.00  
  Purchase #5 $114.65   8.585%   $124.4927   $124.49   $124.50   $124.50  
  Purchase #6 $54.58   11.215%   $60.7011   $60.70   $60.70   $60.70  
  Purchase #7 $146.98   11.550%   $163.9562   $163.96   $163.95   $164.00  
  7 purchase totals = $674.16       $739.4608   $739.45   $739.40   $739.50