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 $49.65   12.282%   $55.748   $55.75   $55.75   $55.70  
  Purchase #2 $204.60   9.859%   $224.7715   $224.77   $224.75   $224.80  
  Purchase #3 $177.87   12.701%   $200.4613   $200.46   $200.45   $200.50  
  Purchase #4 $238.37   11.818%   $266.5406   $266.54   $266.55   $266.50  
  Purchase #5 $126.83   10.548%   $140.208   $140.21   $140.20   $140.20  
  Purchase #6 $95.48   10.305%   $105.3192   $105.32   $105.30   $105.30  
  Purchase #7 $11.74   7.299%   $12.5969   $12.60   $12.60   $12.60  
  7 purchase totals = $904.54       $1,005.6455   $1,005.65   $1,005.60   $1,005.60