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 $68.78   11.176%   $76.4669   $76.47   $76.45   $76.50  
  Purchase #2 $17.78   3.293%   $18.3655   $18.37   $18.35   $18.40  
  Purchase #3 $47.69   11.864%   $53.3479   $53.35   $53.35   $53.30  
  Purchase #4 $102.74   5.584%   $108.477   $108.48   $108.50   $108.50  
  Purchase #5 $109.74   9.661%   $120.342   $120.34   $120.35   $120.30  
  Purchase #6 $223.39   6.557%   $238.0377   $238.04   $238.05   $238.00  
  Purchase #7 $250.68   6.497%   $266.9667   $266.97   $266.95   $267.00  
  7 purchase totals = $820.80       $882.0037   $882.02   $882.00   $882.00