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 $58.96   9.144%   $64.3513   $64.35   $64.35   $64.40  
  Purchase #2 $207.26   5.333%   $218.3132   $218.31   $218.30   $218.30  
  Purchase #3 $64.83   13.693%   $73.7072   $73.71   $73.70   $73.70  
  Purchase #4 $155.51   5.299%   $163.7505   $163.75   $163.75   $163.80  
  Purchase #5 $215.67   8.770%   $234.5843   $234.58   $234.60   $234.60  
  Purchase #6 $250.42   9.655%   $274.5981   $274.60   $274.60   $274.60  
  Purchase #7 $6.55   12.716%   $7.3829   $7.38   $7.40   $7.40  
  7 purchase totals = $959.20       $1,036.6875   $1,036.68   $1,036.70   $1,036.80