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 $48.65   8.131%   $52.6057   $52.61   $52.60   $52.60  
  Purchase #2 $180.43   9.697%   $197.9263   $197.93   $197.95   $197.90  
  Purchase #3 $185.92   12.872%   $209.8516   $209.85   $209.85   $209.90  
  Purchase #4 $55.41   3.543%   $57.3732   $57.37   $57.35   $57.40  
  Purchase #5 $247.48   6.328%   $263.1405   $263.14   $263.15   $263.10  
  Purchase #6 $56.67   6.312%   $60.247   $60.25   $60.25   $60.20  
  Purchase #7 $246.93   12.797%   $278.5296   $278.53   $278.55   $278.50  
  7 purchase totals = $1,021.49       $1,119.6739   $1,119.68   $1,119.70   $1,119.60