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 $120.76   4.631%   $126.3524   $126.35   $126.35   $126.40  
  Purchase #2 $24.94   13.628%   $28.3388   $28.34   $28.35   $28.30  
  Purchase #3 $60.89   5.758%   $64.396   $64.40   $64.40   $64.40  
  Purchase #4 $248.87   10.843%   $275.855   $275.86   $275.85   $275.90  
  Purchase #5 $53.25   4.709%   $55.7575   $55.76   $55.75   $55.80  
  Purchase #6 $249.88   11.531%   $278.6937   $278.69   $278.70   $278.70  
  Purchase #7 $203.67   11.133%   $226.3446   $226.34   $226.35   $226.30  
  7 purchase totals = $962.26       $1,055.7380   $1,055.74   $1,055.75   $1,055.80