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 $23.83   10.590%   $26.3536   $26.35   $26.35   $26.40  
  Purchase #2 $181.50   9.217%   $198.2289   $198.23   $198.25   $198.20  
  Purchase #3 $183.73   12.190%   $206.1267   $206.13   $206.15   $206.10  
  Purchase #4 $246.79   4.274%   $257.3378   $257.34   $257.35   $257.30  
  Purchase #5 $7.51   11.724%   $8.3905   $8.39   $8.40   $8.40  
  Purchase #6 $243.99   10.291%   $269.099   $269.10   $269.10   $269.10  
  Purchase #7 $59.96   13.737%   $68.1967   $68.20   $68.20   $68.20  
  7 purchase totals = $947.31       $1,033.7332   $1,033.74   $1,033.80   $1,033.70