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 $60.75   7.803%   $65.4903   $65.49   $65.50   $65.50  
  Purchase #2 $240.65   5.161%   $253.0699   $253.07   $253.05   $253.10  
  Purchase #3 $183.45   8.219%   $198.5278   $198.53   $198.55   $198.50  
  Purchase #4 $117.47   6.575%   $125.1937   $125.19   $125.20   $125.20  
  Purchase #5 $55.35   6.445%   $58.9173   $58.92   $58.90   $58.90  
  Purchase #6 $151.82   7.430%   $163.1002   $163.10   $163.10   $163.10  
  Purchase #7 $146.40   5.234%   $154.0626   $154.06   $154.05   $154.10  
  7 purchase totals = $955.89       $1,018.3618   $1,018.36   $1,018.35   $1,018.40