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 $92.64   3.147%   $95.5554   $95.56   $95.55   $95.60  
  Purchase #2 $20.71   11.641%   $23.1209   $23.12   $23.10   $23.10  
  Purchase #3 $11.87   8.165%   $12.8392   $12.84   $12.85   $12.80  
  Purchase #4 $84.96   3.820%   $88.2055   $88.21   $88.20   $88.20  
  Purchase #5 $132.26   8.425%   $143.4029   $143.40   $143.40   $143.40  
  Purchase #6 $68.79   13.788%   $78.2748   $78.27   $78.25   $78.30  
  Purchase #7 $229.45   4.676%   $240.1791   $240.18   $240.20   $240.20  
  7 purchase totals = $640.68       $681.5778   $681.58   $681.55   $681.60