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 $244.37   13.394%   $277.1009   $277.10   $277.10   $277.10  
  Purchase #2 $120.63   13.102%   $136.4349   $136.43   $136.45   $136.40  
  Purchase #3 $179.75   13.317%   $203.6873   $203.69   $203.70   $203.70  
  Purchase #4 $228.97   3.324%   $236.581   $236.58   $236.60   $236.60  
  Purchase #5 $116.98   12.118%   $131.1556   $131.16   $131.15   $131.20  
  Purchase #6 $193.36   8.122%   $209.0647   $209.06   $209.05   $209.10  
  Purchase #7 $143.57   8.164%   $155.2911   $155.29   $155.30   $155.30  
  7 purchase totals = $1,227.63       $1,349.3155   $1,349.31   $1,349.35   $1,349.40