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 $241.51   10.119%   $265.9484   $265.95   $265.95   $265.90  
  Purchase #2 $163.89   13.584%   $186.1528   $186.15   $186.15   $186.20  
  Purchase #3 $79.75   13.448%   $90.4748   $90.47   $90.45   $90.50  
  Purchase #4 $89.64   5.475%   $94.5478   $94.55   $94.55   $94.50  
  Purchase #5 $99.32   5.472%   $104.7548   $104.75   $104.75   $104.80  
  Purchase #6 $21.95   12.433%   $24.679   $24.68   $24.70   $24.70  
  Purchase #7 $192.57   5.281%   $202.7396   $202.74   $202.75   $202.70  
  7 purchase totals = $888.63       $969.2972   $969.29   $969.30   $969.30