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 $201.46   4.116%   $209.7521   $209.75   $209.75   $209.80  
  Purchase #2 $212.52   4.599%   $222.2938   $222.29   $222.30   $222.30  
  Purchase #3 $59.64   12.733%   $67.234   $67.23   $67.25   $67.20  
  Purchase #4 $117.61   9.441%   $128.7136   $128.71   $128.70   $128.70  
  Purchase #5 $76.63   6.409%   $81.5412   $81.54   $81.55   $81.50  
  Purchase #6 $200.29   3.228%   $206.7554   $206.76   $206.75   $206.80  
  Purchase #7 $113.53   5.132%   $119.3564   $119.36   $119.35   $119.40  
  7 purchase totals = $981.68       $1,035.6465   $1,035.64   $1,035.65   $1,035.70