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 $141.87   13.462%   $160.9685   $160.97   $160.95   $161.00  
  Purchase #2 $124.51   4.771%   $130.4504   $130.45   $130.45   $130.50  
  Purchase #3 $218.84   3.570%   $226.6526   $226.65   $226.65   $226.70  
  Purchase #4 $236.35   13.681%   $268.685   $268.69   $268.70   $268.70  
  Purchase #5 $229.85   11.191%   $255.5725   $255.57   $255.55   $255.60  
  Purchase #6 $187.45   4.682%   $196.2264   $196.23   $196.25   $196.20  
  Purchase #7 $125.86   10.847%   $139.512   $139.51   $139.50   $139.50  
  7 purchase totals = $1,264.73       $1,378.0674   $1,378.07   $1,378.05   $1,378.20