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 $225.68   12.856%   $254.6934   $254.69   $254.70   $254.70  
  Purchase #2 $116.56   11.228%   $129.6474   $129.65   $129.65   $129.60  
  Purchase #3 $212.46   6.461%   $226.187   $226.19   $226.20   $226.20  
  Purchase #4 $197.27   12.749%   $222.42   $222.42   $222.40   $222.40  
  Purchase #5 $82.83   3.459%   $85.6951   $85.70   $85.70   $85.70  
  Purchase #6 $39.33   3.662%   $40.7703   $40.77   $40.75   $40.80  
  Purchase #7 $179.54   7.681%   $193.3305   $193.33   $193.35   $193.30  
  7 purchase totals = $1,053.67       $1,152.7437   $1,152.75   $1,152.75   $1,152.70