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 $54.68   11.471%   $60.9523   $60.95   $60.95   $61.00  
  Purchase #2 $38.76   4.565%   $40.5294   $40.53   $40.55   $40.50  
  Purchase #3 $198.26   3.665%   $205.5262   $205.53   $205.55   $205.50  
  Purchase #4 $88.99   8.833%   $96.8505   $96.85   $96.85   $96.90  
  Purchase #5 $100.92   5.624%   $106.5957   $106.60   $106.60   $106.60  
  Purchase #6 $10.91   5.372%   $11.4961   $11.50   $11.50   $11.50  
  Purchase #7 $169.40   3.558%   $175.4273   $175.43   $175.45   $175.40  
  7 purchase totals = $661.92       $697.3775   $697.39   $697.45   $697.40