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 $202.50   8.170%   $219.0443   $219.04   $219.05   $219.00  
  Purchase #2 $229.90   4.327%   $239.8478   $239.85   $239.85   $239.80  
  Purchase #3 $56.83   8.591%   $61.7123   $61.71   $61.70   $61.70  
  Purchase #4 $193.37   11.629%   $215.857   $215.86   $215.85   $215.90  
  Purchase #5 $63.60   3.343%   $65.7261   $65.73   $65.75   $65.70  
  Purchase #6 $182.56   4.413%   $190.6164   $190.62   $190.60   $190.60  
  Purchase #7 $228.69   13.171%   $258.8108   $258.81   $258.80   $258.80  
  7 purchase totals = $1,157.45       $1,251.6147   $1,251.62   $1,251.60   $1,251.50