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 $14.45   10.874%   $16.0213   $16.02   $16.00   $16.00  
  Purchase #2 $206.36   11.643%   $230.3865   $230.39   $230.40   $230.40  
  Purchase #3 $27.54   11.546%   $30.7198   $30.72   $30.70   $30.70  
  Purchase #4 $122.97   11.708%   $137.3673   $137.37   $137.35   $137.40  
  Purchase #5 $64.36   5.477%   $67.885   $67.89   $67.90   $67.90  
  Purchase #6 $181.80   12.796%   $205.0631   $205.06   $205.05   $205.10  
  Purchase #7 $7.32   9.270%   $7.9986   $8.00   $8.00   $8.00  
  7 purchase totals = $624.80       $695.4416   $695.45   $695.40   $695.50