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 $52.77   7.324%   $56.6349   $56.63   $56.65   $56.60  
  Purchase #2 $240.63   11.421%   $268.1124   $268.11   $268.10   $268.10  
  Purchase #3 $8.49   10.869%   $9.4128   $9.41   $9.40   $9.40  
  Purchase #4 $78.84   10.645%   $87.2325   $87.23   $87.25   $87.20  
  Purchase #5 $8.37   13.398%   $9.4914   $9.49   $9.50   $9.50  
  Purchase #6 $158.25   13.524%   $179.6517   $179.65   $179.65   $179.70  
  Purchase #7 $196.89   13.303%   $223.0823   $223.08   $223.10   $223.10  
  7 purchase totals = $744.24       $833.6180   $833.60   $833.65   $833.60