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 $67.99   13.236%   $76.9892   $76.99   $77.00   $77.00  
  Purchase #2 $42.31   9.296%   $46.2431   $46.24   $46.25   $46.20  
  Purchase #3 $139.52   5.153%   $146.7095   $146.71   $146.70   $146.70  
  Purchase #4 $86.96   9.263%   $95.0151   $95.02   $95.00   $95.00  
  Purchase #5 $247.96   6.868%   $264.9899   $264.99   $265.00   $265.00  
  Purchase #6 $189.41   9.861%   $208.0877   $208.09   $208.10   $208.10  
  Purchase #7 $157.48   5.296%   $165.8201   $165.82   $165.80   $165.80  
  7 purchase totals = $931.63       $1,003.8546   $1,003.86   $1,003.85   $1,003.80