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 $92.67   10.714%   $102.5987   $102.60   $102.60   $102.60  
  Purchase #2 $114.62   10.631%   $126.8053   $126.81   $126.80   $126.80  
  Purchase #3 $118.54   11.239%   $131.8627   $131.86   $131.85   $131.90  
  Purchase #4 $30.55   11.463%   $34.0519   $34.05   $34.05   $34.10  
  Purchase #5 $84.90   12.320%   $95.3597   $95.36   $95.35   $95.40  
  Purchase #6 $230.71   6.266%   $245.1663   $245.17   $245.15   $245.20  
  Purchase #7 $122.80   13.598%   $139.4983   $139.50   $139.50   $139.50  
  7 purchase totals = $794.79       $875.3429   $875.35   $875.30   $875.50