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 $245.72   11.786%   $274.6806   $274.68   $274.70   $274.70  
  Purchase #2 $144.25   7.614%   $155.2332   $155.23   $155.25   $155.20  
  Purchase #3 $29.86   13.170%   $33.7926   $33.79   $33.80   $33.80  
  Purchase #4 $230.49   7.550%   $247.892   $247.89   $247.90   $247.90  
  Purchase #5 $49.83   5.771%   $52.7057   $52.71   $52.70   $52.70  
  Purchase #6 $210.66   7.567%   $226.6006   $226.60   $226.60   $226.60  
  Purchase #7 $70.27   8.594%   $76.309   $76.31   $76.30   $76.30  
  7 purchase totals = $981.08       $1,067.2137   $1,067.21   $1,067.25   $1,067.20