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 $241.93   12.246%   $271.5567   $271.56   $271.55   $271.60  
  Purchase #2 $31.30   10.411%   $34.5586   $34.56   $34.55   $34.60  
  Purchase #3 $46.30   7.312%   $49.6855   $49.69   $49.70   $49.70  
  Purchase #4 $230.77   3.630%   $239.147   $239.15   $239.15   $239.10  
  Purchase #5 $148.27   12.400%   $166.6555   $166.66   $166.65   $166.70  
  Purchase #6 $183.40   5.380%   $193.2669   $193.27   $193.25   $193.30  
  Purchase #7 $144.80   7.510%   $155.6745   $155.67   $155.65   $155.70  
  7 purchase totals = $1,026.77       $1,110.5447   $1,110.56   $1,110.50   $1,110.70