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 $61.33   12.198%   $68.811   $68.81   $68.80   $68.80  
  Purchase #2 $50.90   5.220%   $53.557   $53.56   $53.55   $53.60  
  Purchase #3 $10.65   6.273%   $11.3181   $11.32   $11.30   $11.30  
  Purchase #4 $248.71   4.220%   $259.2056   $259.21   $259.20   $259.20  
  Purchase #5 $46.56   4.105%   $48.4713   $48.47   $48.45   $48.50  
  Purchase #6 $55.61   13.301%   $63.0067   $63.01   $63.00   $63.00  
  Purchase #7 $17.43   5.118%   $18.3221   $18.32   $18.30   $18.30  
  7 purchase totals = $491.19       $522.6918   $522.70   $522.60   $522.70