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 $54.35   3.619%   $56.3169   $56.32   $56.30   $56.30  
  Purchase #2 $123.79   8.283%   $134.0435   $134.04   $134.05   $134.00  
  Purchase #3 $121.25   4.104%   $126.2261   $126.23   $126.25   $126.20  
  Purchase #4 $250.68   4.418%   $261.755   $261.76   $261.75   $261.80  
  Purchase #5 $112.84   13.559%   $128.14   $128.14   $128.15   $128.10  
  Purchase #6 $31.59   5.299%   $33.264   $33.26   $33.25   $33.30  
  Purchase #7 $195.43   12.123%   $219.122   $219.12   $219.10   $219.10  
  7 purchase totals = $889.93       $958.8675   $958.87   $958.85   $958.80