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 $119.71   6.770%   $127.8144   $127.81   $127.80   $127.80  
  Purchase #2 $159.54   9.792%   $175.1622   $175.16   $175.15   $175.20  
  Purchase #3 $100.83   8.656%   $109.5578   $109.56   $109.55   $109.60  
  Purchase #4 $181.56   11.633%   $202.6809   $202.68   $202.70   $202.70  
  Purchase #5 $175.88   7.307%   $188.7316   $188.73   $188.75   $188.70  
  Purchase #6 $23.61   6.144%   $25.0606   $25.06   $25.05   $25.10  
  Purchase #7 $174.57   11.413%   $194.4937   $194.49   $194.50   $194.50  
  7 purchase totals = $935.70       $1,023.5012   $1,023.49   $1,023.50   $1,023.60