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 $25.27   5.805%   $26.7369   $26.74   $26.75   $26.70  
  Purchase #2 $177.27   3.656%   $183.751   $183.75   $183.75   $183.80  
  Purchase #3 $126.70   12.659%   $142.739   $142.74   $142.75   $142.70  
  Purchase #4 $50.70   12.292%   $56.932   $56.93   $56.95   $56.90  
  Purchase #5 $194.31   5.466%   $204.931   $204.93   $204.95   $204.90  
  Purchase #6 $47.58   11.730%   $53.1611   $53.16   $53.15   $53.20  
  Purchase #7 $140.86   12.654%   $158.6844   $158.68   $158.70   $158.70  
  7 purchase totals = $762.69       $826.9354   $826.93   $827.00   $826.90