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 $242.72   10.786%   $268.8998   $268.90   $268.90   $268.90  
  Purchase #2 $190.91   6.186%   $202.7197   $202.72   $202.70   $202.70  
  Purchase #3 $87.67   7.270%   $94.0436   $94.04   $94.05   $94.00  
  Purchase #4 $175.69   11.628%   $196.1192   $196.12   $196.10   $196.10  
  Purchase #5 $179.88   7.740%   $193.8027   $193.80   $193.80   $193.80  
  Purchase #6 $61.31   4.249%   $63.9151   $63.92   $63.90   $63.90  
  Purchase #7 $202.33   11.329%   $225.252   $225.25   $225.25   $225.30  
  7 purchase totals = $1,140.51       $1,244.7521   $1,244.75   $1,244.70   $1,244.70