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 $70.85   6.693%   $75.592   $75.59   $75.60   $75.60  
  Purchase #2 $248.76   3.756%   $258.1034   $258.10   $258.10   $258.10  
  Purchase #3 $73.56   4.301%   $76.7238   $76.72   $76.70   $76.70  
  Purchase #4 $58.83   7.676%   $63.3458   $63.35   $63.35   $63.30  
  Purchase #5 $235.75   4.471%   $246.2904   $246.29   $246.30   $246.30  
  Purchase #6 $11.36   5.662%   $12.0032   $12.00   $12.00   $12.00  
  Purchase #7 $158.46   9.624%   $173.7102   $173.71   $173.70   $173.70  
  7 purchase totals = $857.57       $905.7688   $905.76   $905.75   $905.70