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 $242.78   6.655%   $258.937   $258.94   $258.95   $258.90  
  Purchase #2 $170.54   13.615%   $193.759   $193.76   $193.75   $193.80  
  Purchase #3 $56.96   6.449%   $60.6334   $60.63   $60.65   $60.60  
  Purchase #4 $208.57   10.386%   $230.2321   $230.23   $230.25   $230.20  
  Purchase #5 $67.93   8.731%   $73.861   $73.86   $73.85   $73.90  
  Purchase #6 $198.76   3.700%   $206.1141   $206.11   $206.10   $206.10  
  Purchase #7 $22.34   10.709%   $24.7324   $24.73   $24.75   $24.70  
  7 purchase totals = $967.88       $1,048.2690   $1,048.26   $1,048.30   $1,048.20