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 $34.98   10.242%   $38.5627   $38.56   $38.55   $38.60  
  Purchase #2 $97.94   9.538%   $107.2815   $107.28   $107.30   $107.30  
  Purchase #3 $42.53   6.808%   $45.4254   $45.43   $45.45   $45.40  
  Purchase #4 $67.76   6.849%   $72.4009   $72.40   $72.40   $72.40  
  Purchase #5 $125.43   10.850%   $139.0392   $139.04   $139.05   $139.00  
  Purchase #6 $191.74   11.570%   $213.9243   $213.92   $213.90   $213.90  
  Purchase #7 $219.48   7.554%   $236.0595   $236.06   $236.05   $236.10  
  7 purchase totals = $779.86       $852.6935   $852.69   $852.70   $852.70