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 $63.83   8.104%   $69.0028   $69.00   $69.00   $69.00  
  Purchase #2 $235.98   8.773%   $256.6825   $256.68   $256.70   $256.70  
  Purchase #3 $73.39   13.605%   $83.3747   $83.37   $83.35   $83.40  
  Purchase #4 $80.25   4.277%   $83.6823   $83.68   $83.70   $83.70  
  Purchase #5 $184.68   11.294%   $205.5378   $205.54   $205.55   $205.50  
  Purchase #6 $61.72   3.204%   $63.6975   $63.70   $63.70   $63.70  
  Purchase #7 $44.99   8.183%   $48.6715   $48.67   $48.65   $48.70  
  7 purchase totals = $744.84       $810.6491   $810.64   $810.65   $810.70