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 $52.82   7.331%   $56.6922   $56.69   $56.70   $56.70  
  Purchase #2 $32.87   7.838%   $35.4464   $35.45   $35.45   $35.40  
  Purchase #3 $178.98   10.670%   $198.0772   $198.08   $198.10   $198.10  
  Purchase #4 $64.46   4.487%   $67.3523   $67.35   $67.35   $67.40  
  Purchase #5 $98.39   11.149%   $109.3595   $109.36   $109.35   $109.40  
  Purchase #6 $163.75   3.426%   $169.3601   $169.36   $169.35   $169.40  
  Purchase #7 $243.89   6.430%   $259.5721   $259.57   $259.55   $259.60  
  7 purchase totals = $835.16       $895.8598   $895.86   $895.85   $896.00