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 $180.81   13.218%   $204.7095   $204.71   $204.70   $204.70  
  Purchase #2 $187.30   3.656%   $194.1477   $194.15   $194.15   $194.10  
  Purchase #3 $53.47   9.826%   $58.724   $58.72   $58.70   $58.70  
  Purchase #4 $193.76   7.214%   $207.7378   $207.74   $207.75   $207.70  
  Purchase #5 $186.65   8.702%   $202.8923   $202.89   $202.90   $202.90  
  Purchase #6 $206.89   8.382%   $224.2315   $224.23   $224.25   $224.20  
  Purchase #7 $84.83   4.502%   $88.649   $88.65   $88.65   $88.60  
  7 purchase totals = $1,093.71       $1,181.0918   $1,181.09   $1,181.10   $1,180.90