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 $76.31   6.467%   $81.245   $81.25   $81.25   $81.20  
  Purchase #2 $63.44   7.459%   $68.172   $68.17   $68.15   $68.20  
  Purchase #3 $169.56   13.694%   $192.7795   $192.78   $192.80   $192.80  
  Purchase #4 $103.25   9.431%   $112.9875   $112.99   $113.00   $113.00  
  Purchase #5 $239.60   8.338%   $259.5778   $259.58   $259.60   $259.60  
  Purchase #6 $46.85   6.414%   $49.855   $49.86   $49.85   $49.90  
  Purchase #7 $231.81   11.738%   $259.0199   $259.02   $259.00   $259.00  
  7 purchase totals = $930.82       $1,023.6367   $1,023.65   $1,023.65   $1,023.70