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 $91.54   5.172%   $96.2744   $96.27   $96.25   $96.30  
  Purchase #2 $247.34   4.848%   $259.331   $259.33   $259.35   $259.30  
  Purchase #3 $129.98   7.141%   $139.2619   $139.26   $139.25   $139.30  
  Purchase #4 $157.46   3.144%   $162.4105   $162.41   $162.40   $162.40  
  Purchase #5 $149.59   5.233%   $157.418   $157.42   $157.40   $157.40  
  Purchase #6 $235.95   4.281%   $246.051   $246.05   $246.05   $246.10  
  Purchase #7 $207.54   8.676%   $225.5462   $225.55   $225.55   $225.50  
  7 purchase totals = $1,219.40       $1,286.2930   $1,286.29   $1,286.25   $1,286.30