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 $87.57   9.481%   $95.8725   $95.87   $95.85   $95.90  
  Purchase #2 $77.33   9.496%   $84.6733   $84.67   $84.65   $84.70  
  Purchase #3 $241.83   10.110%   $266.279   $266.28   $266.30   $266.30  
  Purchase #4 $76.87   4.426%   $80.2723   $80.27   $80.25   $80.30  
  Purchase #5 $193.88   7.527%   $208.4733   $208.47   $208.45   $208.50  
  Purchase #6 $205.25   8.461%   $222.6162   $222.62   $222.60   $222.60  
  Purchase #7 $69.93   8.284%   $75.723   $75.72   $75.70   $75.70  
  7 purchase totals = $952.66       $1,033.9096   $1,033.90   $1,033.80   $1,034.00