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 $241.48   10.712%   $267.3473   $267.35   $267.35   $267.30  
  Purchase #2 $187.95   5.192%   $197.7084   $197.71   $197.70   $197.70  
  Purchase #3 $42.33   3.321%   $43.7358   $43.74   $43.75   $43.70  
  Purchase #4 $24.25   7.475%   $26.0627   $26.06   $26.05   $26.10  
  Purchase #5 $186.78   6.789%   $199.4605   $199.46   $199.45   $199.50  
  Purchase #6 $106.50   3.857%   $110.6077   $110.61   $110.60   $110.60  
  Purchase #7 $86.81   6.211%   $92.2018   $92.20   $92.20   $92.20  
  7 purchase totals = $876.10       $937.1242   $937.13   $937.10   $937.10