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 $167.97   11.176%   $186.7423   $186.74   $186.75   $186.70  
  Purchase #2 $220.97   9.693%   $242.3886   $242.39   $242.40   $242.40  
  Purchase #3 $103.68   6.342%   $110.2554   $110.26   $110.25   $110.30  
  Purchase #4 $41.72   13.667%   $47.4219   $47.42   $47.40   $47.40  
  Purchase #5 $186.35   6.864%   $199.1411   $199.14   $199.15   $199.10  
  Purchase #6 $169.97   8.706%   $184.7676   $184.77   $184.75   $184.80  
  Purchase #7 $86.83   5.319%   $91.4485   $91.45   $91.45   $91.40  
  7 purchase totals = $977.49       $1,062.1654   $1,062.17   $1,062.15   $1,062.10