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 $188.58   8.816%   $205.2052   $205.21   $205.20   $205.20  
  Purchase #2 $46.60   11.609%   $52.0098   $52.01   $52.00   $52.00  
  Purchase #3 $83.32   8.471%   $90.378   $90.38   $90.40   $90.40  
  Purchase #4 $130.84   3.124%   $134.9274   $134.93   $134.95   $134.90  
  Purchase #5 $242.85   13.648%   $275.9942   $275.99   $276.00   $276.00  
  Purchase #6 $247.54   13.808%   $281.7203   $281.72   $281.70   $281.70  
  Purchase #7 $125.38   8.664%   $136.2429   $136.24   $136.25   $136.20  
  7 purchase totals = $1,065.11       $1,176.4778   $1,176.48   $1,176.50   $1,176.40