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 $208.85   5.524%   $220.3869   $220.39   $220.40   $220.40  
  Purchase #2 $146.75   10.434%   $162.0619   $162.06   $162.05   $162.10  
  Purchase #3 $219.82   9.577%   $240.8722   $240.87   $240.85   $240.90  
  Purchase #4 $139.49   12.315%   $156.6682   $156.67   $156.65   $156.70  
  Purchase #5 $11.86   9.474%   $12.9836   $12.98   $13.00   $13.00  
  Purchase #6 $137.81   5.672%   $145.6266   $145.63   $145.65   $145.60  
  Purchase #7 $191.31   12.205%   $214.6594   $214.66   $214.65   $214.70  
  7 purchase totals = $1,055.89       $1,153.2588   $1,153.26   $1,153.25   $1,153.40