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 $240.40   5.247%   $253.0138   $253.01   $253.00   $253.00  
  Purchase #2 $185.96   5.644%   $196.4556   $196.46   $196.45   $196.50  
  Purchase #3 $238.32   5.306%   $250.9653   $250.97   $250.95   $251.00  
  Purchase #4 $39.47   12.574%   $44.433   $44.43   $44.45   $44.40  
  Purchase #5 $82.99   7.542%   $89.2491   $89.25   $89.25   $89.20  
  Purchase #6 $147.58   12.623%   $166.209   $166.21   $166.20   $166.20  
  Purchase #7 $23.53   11.511%   $26.2385   $26.24   $26.25   $26.20  
  7 purchase totals = $958.25       $1,026.5643   $1,026.57   $1,026.55   $1,026.50