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 $57.77   13.518%   $65.5793   $65.58   $65.60   $65.60  
  Purchase #2 $184.56   6.543%   $196.6358   $196.64   $196.65   $196.60  
  Purchase #3 $24.63   12.378%   $27.6787   $27.68   $27.70   $27.70  
  Purchase #4 $92.49   13.651%   $105.1158   $105.12   $105.10   $105.10  
  Purchase #5 $139.29   9.824%   $152.9738   $152.97   $152.95   $153.00  
  Purchase #6 $232.81   3.716%   $241.4612   $241.46   $241.45   $241.50  
  Purchase #7 $25.65   3.706%   $26.6006   $26.60   $26.60   $26.60  
  7 purchase totals = $757.20       $816.0452   $816.05   $816.05   $816.10