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 $106.92   10.602%   $118.2557   $118.26   $118.25   $118.30  
  Purchase #2 $131.99   7.488%   $141.8734   $141.87   $141.85   $141.90  
  Purchase #3 $222.43   11.841%   $248.7679   $248.77   $248.75   $248.80  
  Purchase #4 $228.85   7.294%   $245.5423   $245.54   $245.55   $245.50  
  Purchase #5 $131.99   12.232%   $148.135   $148.14   $148.15   $148.10  
  Purchase #6 $27.39   5.800%   $28.9786   $28.98   $29.00   $29.00  
  Purchase #7 $35.95   7.750%   $38.7361   $38.74   $38.75   $38.70  
  7 purchase totals = $885.52       $970.2890   $970.30   $970.30   $970.30