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 $208.68   12.822%   $235.4369   $235.44   $235.45   $235.40  
  Purchase #2 $224.39   5.192%   $236.0403   $236.04   $236.05   $236.00  
  Purchase #3 $193.65   11.354%   $215.637   $215.64   $215.65   $215.60  
  Purchase #4 $55.64   13.811%   $63.3244   $63.32   $63.30   $63.30  
  Purchase #5 $71.67   9.618%   $78.5632   $78.56   $78.55   $78.60  
  Purchase #6 $45.98   6.395%   $48.9204   $48.92   $48.90   $48.90  
  Purchase #7 $191.55   11.207%   $213.017   $213.02   $213.00   $213.00  
  7 purchase totals = $991.56       $1,090.9392   $1,090.94   $1,090.90   $1,090.80