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 $176.57   10.621%   $195.3235   $195.32   $195.30   $195.30  
  Purchase #2 $56.47   12.727%   $63.6569   $63.66   $63.65   $63.70  
  Purchase #3 $213.68   10.447%   $236.0031   $236.00   $236.00   $236.00  
  Purchase #4 $143.54   6.732%   $153.2031   $153.20   $153.20   $153.20  
  Purchase #5 $15.68   6.115%   $16.6388   $16.64   $16.65   $16.60  
  Purchase #6 $121.93   11.549%   $136.0117   $136.01   $136.00   $136.00  
  Purchase #7 $231.88   11.182%   $257.8088   $257.81   $257.80   $257.80  
  7 purchase totals = $959.75       $1,058.6459   $1,058.64   $1,058.60   $1,058.60