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 $149.86   11.239%   $166.7028   $166.70   $166.70   $166.70  
  Purchase #2 $205.83   10.228%   $226.8823   $226.88   $226.90   $226.90  
  Purchase #3 $74.45   12.512%   $83.7652   $83.77   $83.75   $83.80  
  Purchase #4 $19.91   5.826%   $21.07   $21.07   $21.05   $21.10  
  Purchase #5 $178.32   8.462%   $193.4094   $193.41   $193.40   $193.40  
  Purchase #6 $92.86   12.627%   $104.5854   $104.59   $104.60   $104.60  
  Purchase #7 $205.36   5.577%   $216.8129   $216.81   $216.80   $216.80  
  7 purchase totals = $926.59       $1,013.2280   $1,013.23   $1,013.20   $1,013.30