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 $173.54   5.713%   $183.4543   $183.45   $183.45   $183.50  
  Purchase #2 $167.31   6.405%   $178.0262   $178.03   $178.05   $178.00  
  Purchase #3 $118.91   5.870%   $125.89   $125.89   $125.90   $125.90  
  Purchase #4 $215.34   10.334%   $237.5932   $237.59   $237.60   $237.60  
  Purchase #5 $59.80   11.105%   $66.4408   $66.44   $66.45   $66.40  
  Purchase #6 $28.92   4.458%   $30.2093   $30.21   $30.20   $30.20  
  Purchase #7 $133.71   3.719%   $138.6827   $138.68   $138.70   $138.70  
  7 purchase totals = $897.53       $960.2965   $960.29   $960.35   $960.30