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 $76.91   8.157%   $83.1835   $83.18   $83.20   $83.20  
  Purchase #2 $193.78   7.189%   $207.7108   $207.71   $207.70   $207.70  
  Purchase #3 $182.51   3.696%   $189.2556   $189.26   $189.25   $189.30  
  Purchase #4 $12.80   13.669%   $14.5496   $14.55   $14.55   $14.50  
  Purchase #5 $235.71   8.644%   $256.0848   $256.08   $256.10   $256.10  
  Purchase #6 $5.38   8.423%   $5.8332   $5.83   $5.85   $5.80  
  Purchase #7 $245.55   8.436%   $266.2646   $266.26   $266.25   $266.30  
  7 purchase totals = $952.64       $1,022.8821   $1,022.87   $1,022.90   $1,022.90