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 $228.47   10.502%   $252.4639   $252.46   $252.45   $252.50  
  Purchase #2 $53.59   11.456%   $59.7293   $59.73   $59.75   $59.70  
  Purchase #3 $62.79   10.129%   $69.15   $69.15   $69.15   $69.20  
  Purchase #4 $24.43   9.703%   $26.8004   $26.80   $26.80   $26.80  
  Purchase #5 $85.94   6.560%   $91.5777   $91.58   $91.60   $91.60  
  Purchase #6 $196.99   10.699%   $218.066   $218.07   $218.05   $218.10  
  Purchase #7 $228.61   4.819%   $239.6267   $239.63   $239.65   $239.60  
  7 purchase totals = $880.82       $957.4140   $957.42   $957.45   $957.50