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 $111.77   12.742%   $126.0117   $126.01   $126.00   $126.00  
  Purchase #2 $95.48   7.307%   $102.4567   $102.46   $102.45   $102.50  
  Purchase #3 $144.84   6.244%   $153.8838   $153.88   $153.90   $153.90  
  Purchase #4 $140.64   4.323%   $146.7199   $146.72   $146.70   $146.70  
  Purchase #5 $142.49   8.711%   $154.9023   $154.90   $154.90   $154.90  
  Purchase #6 $219.30   7.410%   $235.5501   $235.55   $235.55   $235.60  
  Purchase #7 $164.69   8.725%   $179.0592   $179.06   $179.05   $179.10  
  7 purchase totals = $1,019.21       $1,098.5837   $1,098.58   $1,098.55   $1,098.70