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 $58.77   4.639%   $61.4963   $61.50   $61.50   $61.50  
  Purchase #2 $8.76   10.820%   $9.7078   $9.71   $9.70   $9.70  
  Purchase #3 $213.75   5.643%   $225.8119   $225.81   $225.80   $225.80  
  Purchase #4 $55.74   10.543%   $61.6167   $61.62   $61.60   $61.60  
  Purchase #5 $64.87   5.724%   $68.5832   $68.58   $68.60   $68.60  
  Purchase #6 $41.67   12.630%   $46.9329   $46.93   $46.95   $46.90  
  Purchase #7 $56.68   7.717%   $61.054   $61.05   $61.05   $61.10  
  7 purchase totals = $500.24       $535.2028   $535.20   $535.20   $535.20