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 $246.60   3.269%   $254.6614   $254.66   $254.65   $254.70  
  Purchase #2 $64.79   10.261%   $71.4381   $71.44   $71.45   $71.40  
  Purchase #3 $102.95   12.728%   $116.0535   $116.05   $116.05   $116.10  
  Purchase #4 $188.31   9.134%   $205.5102   $205.51   $205.50   $205.50  
  Purchase #5 $77.54   6.306%   $82.4297   $82.43   $82.45   $82.40  
  Purchase #6 $164.26   13.609%   $186.6141   $186.61   $186.60   $186.60  
  Purchase #7 $228.39   13.146%   $258.4141   $258.41   $258.40   $258.40  
  7 purchase totals = $1,072.84       $1,175.1211   $1,175.11   $1,175.10   $1,175.10