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 $197.40   4.843%   $206.9601   $206.96   $206.95   $207.00  
  Purchase #2 $63.54   11.232%   $70.6768   $70.68   $70.70   $70.70  
  Purchase #3 $203.78   5.468%   $214.9227   $214.92   $214.90   $214.90  
  Purchase #4 $166.97   6.273%   $177.444   $177.44   $177.45   $177.40  
  Purchase #5 $35.96   4.382%   $37.5358   $37.54   $37.55   $37.50  
  Purchase #6 $221.44   3.406%   $228.9822   $228.98   $229.00   $229.00  
  Purchase #7 $49.44   9.342%   $54.0587   $54.06   $54.05   $54.10  
  7 purchase totals = $938.53       $990.5803   $990.58   $990.60   $990.60