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 $191.58   7.258%   $205.4849   $205.48   $205.50   $205.50  
  Purchase #2 $158.39   13.473%   $179.7299   $179.73   $179.75   $179.70  
  Purchase #3 $126.39   9.725%   $138.6814   $138.68   $138.70   $138.70  
  Purchase #4 $87.98   8.854%   $95.7697   $95.77   $95.75   $95.80  
  Purchase #5 $152.83   6.814%   $163.2438   $163.24   $163.25   $163.20  
  Purchase #6 $72.98   5.506%   $76.9983   $77.00   $77.00   $77.00  
  Purchase #7 $95.53   10.517%   $105.5769   $105.58   $105.60   $105.60  
  7 purchase totals = $885.68       $965.4849   $965.48   $965.55   $965.50