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 $93.78   10.380%   $103.5144   $103.51   $103.50   $103.50  
  Purchase #2 $74.57   8.691%   $81.0509   $81.05   $81.05   $81.10  
  Purchase #3 $231.70   7.418%   $248.8875   $248.89   $248.90   $248.90  
  Purchase #4 $58.65   7.832%   $63.2435   $63.24   $63.25   $63.20  
  Purchase #5 $238.81   4.828%   $250.3397   $250.34   $250.35   $250.30  
  Purchase #6 $53.79   10.616%   $59.5003   $59.50   $59.50   $59.50  
  Purchase #7 $143.43   5.361%   $151.1193   $151.12   $151.10   $151.10  
  7 purchase totals = $894.73       $957.6556   $957.65   $957.65   $957.60