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 $58.62   13.371%   $66.4581   $66.46   $66.45   $66.50  
  Purchase #2 $157.33   10.190%   $173.3619   $173.36   $173.35   $173.40  
  Purchase #3 $207.67   5.269%   $218.6121   $218.61   $218.60   $218.60  
  Purchase #4 $122.93   7.124%   $131.6875   $131.69   $131.70   $131.70  
  Purchase #5 $179.77   6.655%   $191.7337   $191.73   $191.75   $191.70  
  Purchase #6 $233.95   13.575%   $265.7087   $265.71   $265.70   $265.70  
  Purchase #7 $88.57   13.697%   $100.7014   $100.70   $100.70   $100.70  
  7 purchase totals = $1,048.84       $1,148.2634   $1,148.26   $1,148.25   $1,148.30