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 $187.57   9.581%   $205.5411   $205.54   $205.55   $205.50  
  Purchase #2 $95.58   8.481%   $103.6861   $103.69   $103.70   $103.70  
  Purchase #3 $107.31   9.244%   $117.2297   $117.23   $117.25   $117.20  
  Purchase #4 $91.67   3.567%   $94.9399   $94.94   $94.95   $94.90  
  Purchase #5 $50.43   5.611%   $53.2596   $53.26   $53.25   $53.30  
  Purchase #6 $184.69   11.106%   $205.2017   $205.20   $205.20   $205.20  
  Purchase #7 $201.96   12.367%   $226.9364   $226.94   $226.95   $226.90  
  7 purchase totals = $919.21       $1,006.7945   $1,006.80   $1,006.85   $1,006.70