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 $58.41   5.238%   $61.4695   $61.47   $61.45   $61.50  
  Purchase #2 $202.67   11.862%   $226.7107   $226.71   $226.70   $226.70  
  Purchase #3 $73.51   6.381%   $78.2007   $78.20   $78.20   $78.20  
  Purchase #4 $183.97   13.759%   $209.2824   $209.28   $209.30   $209.30  
  Purchase #5 $19.89   8.841%   $21.6485   $21.65   $21.65   $21.60  
  Purchase #6 $28.51   13.783%   $32.4395   $32.44   $32.45   $32.40  
  Purchase #7 $125.32   3.288%   $129.4405   $129.44   $129.45   $129.40  
  7 purchase totals = $692.28       $759.1918   $759.19   $759.20   $759.10