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 $58.31   3.859%   $60.5602   $60.56   $60.55   $60.60  
  Purchase #2 $26.25   4.454%   $27.4192   $27.42   $27.40   $27.40  
  Purchase #3 $208.89   7.234%   $224.0011   $224.00   $224.00   $224.00  
  Purchase #4 $8.53   3.706%   $8.8461   $8.85   $8.85   $8.80  
  Purchase #5 $219.68   6.153%   $233.1969   $233.20   $233.20   $233.20  
  Purchase #6 $65.89   3.508%   $68.2014   $68.20   $68.20   $68.20  
  Purchase #7 $107.67   4.267%   $112.2643   $112.26   $112.25   $112.30  
  7 purchase totals = $695.22       $734.4892   $734.49   $734.45   $734.50