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 $239.45   13.195%   $271.0454   $271.05   $271.05   $271.00  
  Purchase #2 $177.91   13.437%   $201.8158   $201.82   $201.80   $201.80  
  Purchase #3 $74.77   11.249%   $83.1809   $83.18   $83.20   $83.20  
  Purchase #4 $146.97   12.285%   $165.0253   $165.03   $165.05   $165.00  
  Purchase #5 $132.82   10.592%   $146.8883   $146.89   $146.90   $146.90  
  Purchase #6 $182.49   5.533%   $192.5872   $192.59   $192.60   $192.60  
  Purchase #7 $134.88   9.868%   $148.19   $148.19   $148.20   $148.20  
  7 purchase totals = $1,089.29       $1,208.7329   $1,208.75   $1,208.80   $1,208.70