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 $205.48   8.872%   $223.7102   $223.71   $223.70   $223.70  
  Purchase #2 $14.34   6.293%   $15.2424   $15.24   $15.25   $15.20  
  Purchase #3 $95.48   9.558%   $104.606   $104.61   $104.60   $104.60  
  Purchase #4 $191.60   6.738%   $204.51   $204.51   $204.50   $204.50  
  Purchase #5 $66.54   8.670%   $72.309   $72.31   $72.30   $72.30  
  Purchase #6 $167.74   5.654%   $177.224   $177.22   $177.20   $177.20  
  Purchase #7 $167.26   11.577%   $186.6237   $186.62   $186.60   $186.60  
  7 purchase totals = $908.44       $984.2253   $984.22   $984.15   $984.10