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 $60.92   11.588%   $67.9794   $67.98   $68.00   $68.00  
  Purchase #2 $59.92   6.681%   $63.9233   $63.92   $63.90   $63.90  
  Purchase #3 $58.66   7.822%   $63.2484   $63.25   $63.25   $63.20  
  Purchase #4 $90.70   6.290%   $96.405   $96.41   $96.40   $96.40  
  Purchase #5 $53.98   3.519%   $55.8796   $55.88   $55.90   $55.90  
  Purchase #6 $6.83   12.426%   $7.6787   $7.68   $7.70   $7.70  
  Purchase #7 $12.72   13.413%   $14.4261   $14.43   $14.45   $14.40  
  7 purchase totals = $343.73       $369.5405   $369.55   $369.60   $369.50