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 $246.43   5.303%   $259.4982   $259.50   $259.50   $259.50  
  Purchase #2 $147.79   6.602%   $157.5471   $157.55   $157.55   $157.50  
  Purchase #3 $119.75   12.493%   $134.7104   $134.71   $134.70   $134.70  
  Purchase #4 $108.97   11.574%   $121.5822   $121.58   $121.60   $121.60  
  Purchase #5 $81.61   6.684%   $87.0648   $87.06   $87.05   $87.10  
  Purchase #6 $208.86   8.481%   $226.5734   $226.57   $226.55   $226.60  
  Purchase #7 $65.45   9.297%   $71.5349   $71.53   $71.55   $71.50  
  7 purchase totals = $978.86       $1,058.5110   $1,058.50   $1,058.50   $1,058.50