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 $61.59   8.191%   $66.6348   $66.63   $66.65   $66.60  
  Purchase #2 $112.37   3.734%   $116.5659   $116.57   $116.55   $116.60  
  Purchase #3 $35.75   6.371%   $38.0276   $38.03   $38.05   $38.00  
  Purchase #4 $78.92   4.236%   $82.2631   $82.26   $82.25   $82.30  
  Purchase #5 $165.26   10.623%   $182.8156   $182.82   $182.80   $182.80  
  Purchase #6 $8.94   13.498%   $10.1467   $10.15   $10.15   $10.10  
  Purchase #7 $44.70   5.119%   $46.9882   $46.99   $47.00   $47.00  
  7 purchase totals = $507.53       $543.4419   $543.45   $543.45   $543.40