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 $228.26   9.284%   $249.4517   $249.45   $249.45   $249.50  
  Purchase #2 $157.89   6.242%   $167.7455   $167.75   $167.75   $167.70  
  Purchase #3 $151.31   7.706%   $162.9699   $162.97   $162.95   $163.00  
  Purchase #4 $159.42   7.533%   $171.4291   $171.43   $171.45   $171.40  
  Purchase #5 $14.97   10.217%   $16.4995   $16.50   $16.50   $16.50  
  Purchase #6 $98.95   6.114%   $104.9998   $105.00   $105.00   $105.00  
  Purchase #7 $150.65   9.216%   $164.5339   $164.53   $164.55   $164.50  
  7 purchase totals = $961.45       $1,037.6294   $1,037.63   $1,037.65   $1,037.60