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 $113.69   10.287%   $125.3853   $125.39   $125.40   $125.40  
  Purchase #2 $209.39   3.706%   $217.15   $217.15   $217.15   $217.20  
  Purchase #3 $107.99   12.470%   $121.4564   $121.46   $121.45   $121.50  
  Purchase #4 $229.63   3.857%   $238.4868   $238.49   $238.50   $238.50  
  Purchase #5 $86.51   9.402%   $94.6437   $94.64   $94.65   $94.60  
  Purchase #6 $140.79   11.255%   $156.6359   $156.64   $156.65   $156.60  
  Purchase #7 $125.93   7.864%   $135.8331   $135.83   $135.85   $135.80  
  7 purchase totals = $1,013.93       $1,089.5912   $1,089.60   $1,089.65   $1,089.60