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 $23.74   3.522%   $24.5761   $24.58   $24.60   $24.60  
  Purchase #2 $205.37   12.334%   $230.7003   $230.70   $230.70   $230.70  
  Purchase #3 $165.91   13.866%   $188.9151   $188.92   $188.90   $188.90  
  Purchase #4 $244.26   11.711%   $272.8653   $272.87   $272.85   $272.90  
  Purchase #5 $71.50   13.236%   $80.9637   $80.96   $80.95   $81.00  
  Purchase #6 $79.81   4.682%   $83.5467   $83.55   $83.55   $83.50  
  Purchase #7 $116.69   5.791%   $123.4475   $123.45   $123.45   $123.40  
  7 purchase totals = $907.28       $1,005.0147   $1,005.03   $1,005.00   $1,005.00