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 $249.52   5.291%   $262.7221   $262.72   $262.70   $262.70  
  Purchase #2 $124.31   6.279%   $132.1154   $132.12   $132.10   $132.10  
  Purchase #3 $8.26   5.353%   $8.7022   $8.70   $8.70   $8.70  
  Purchase #4 $245.58   5.299%   $258.5933   $258.59   $258.60   $258.60  
  Purchase #5 $29.89   7.234%   $32.0522   $32.05   $32.05   $32.10  
  Purchase #6 $24.53   12.629%   $27.6279   $27.63   $27.65   $27.60  
  Purchase #7 $52.28   5.342%   $55.0728   $55.07   $55.05   $55.10  
  7 purchase totals = $734.37       $776.8859   $776.88   $776.85   $776.90