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 $58.58   6.260%   $62.2471   $62.25   $62.25   $62.20  
  Purchase #2 $229.28   9.790%   $251.7265   $251.73   $251.75   $251.70  
  Purchase #3 $155.39   4.696%   $162.6871   $162.69   $162.70   $162.70  
  Purchase #4 $28.81   12.619%   $32.4455   $32.45   $32.45   $32.40  
  Purchase #5 $175.63   5.208%   $184.7768   $184.78   $184.80   $184.80  
  Purchase #6 $42.76   13.544%   $48.5514   $48.55   $48.55   $48.60  
  Purchase #7 $96.39   11.396%   $107.3746   $107.37   $107.35   $107.40  
  7 purchase totals = $786.84       $849.8090   $849.82   $849.85   $849.80