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 $16.86   4.403%   $17.6023   $17.60   $17.60   $17.60  
  Purchase #2 $170.66   3.167%   $176.0648   $176.06   $176.05   $176.10  
  Purchase #3 $247.86   3.737%   $257.1225   $257.12   $257.10   $257.10  
  Purchase #4 $76.93   8.507%   $83.4744   $83.47   $83.45   $83.50  
  Purchase #5 $161.94   5.358%   $170.6167   $170.62   $170.60   $170.60  
  Purchase #6 $202.31   11.745%   $226.0713   $226.07   $226.05   $226.10  
  Purchase #7 $240.25   9.206%   $262.3674   $262.37   $262.35   $262.40  
  7 purchase totals = $1,116.81       $1,193.3194   $1,193.31   $1,193.20   $1,193.40