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 $188.75   9.435%   $206.5586   $206.56   $206.55   $206.60  
  Purchase #2 $232.46   7.542%   $249.9921   $249.99   $250.00   $250.00  
  Purchase #3 $11.33   10.823%   $12.5562   $12.56   $12.55   $12.60  
  Purchase #4 $159.66   12.173%   $179.0954   $179.10   $179.10   $179.10  
  Purchase #5 $51.48   7.274%   $55.2247   $55.22   $55.20   $55.20  
  Purchase #6 $69.88   11.580%   $77.9721   $77.97   $77.95   $78.00  
  Purchase #7 $196.58   4.172%   $204.7813   $204.78   $204.80   $204.80  
  7 purchase totals = $910.14       $986.1804   $986.18   $986.15   $986.30