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 $188.65   9.738%   $207.0207   $207.02   $207.00   $207.00  
  Purchase #2 $166.27   12.625%   $187.2616   $187.26   $187.25   $187.30  
  Purchase #3 $8.81   7.184%   $9.4429   $9.44   $9.45   $9.40  
  Purchase #4 $163.97   13.777%   $186.5601   $186.56   $186.55   $186.60  
  Purchase #5 $62.99   9.577%   $69.0226   $69.02   $69.00   $69.00  
  Purchase #6 $115.72   8.374%   $125.4104   $125.41   $125.40   $125.40  
  Purchase #7 $59.66   12.748%   $67.2655   $67.27   $67.25   $67.30  
  7 purchase totals = $766.07       $851.9838   $851.98   $851.90   $852.00