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 $228.67   10.541%   $252.7741   $252.77   $252.75   $252.80  
  Purchase #2 $208.91   11.835%   $233.6345   $233.63   $233.65   $233.60  
  Purchase #3 $167.36   7.232%   $179.4635   $179.46   $179.45   $179.50  
  Purchase #4 $10.37   5.796%   $10.971   $10.97   $10.95   $11.00  
  Purchase #5 $198.61   10.225%   $218.9179   $218.92   $218.90   $218.90  
  Purchase #6 $243.86   8.427%   $264.4101   $264.41   $264.40   $264.40  
  Purchase #7 $201.42   4.775%   $211.0378   $211.04   $211.05   $211.00  
  7 purchase totals = $1,259.20       $1,371.2089   $1,371.20   $1,371.15   $1,371.20