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 $161.43   9.806%   $177.2598   $177.26   $177.25   $177.30  
  Purchase #2 $127.96   8.837%   $139.2678   $139.27   $139.25   $139.30  
  Purchase #3 $197.37   3.171%   $203.6286   $203.63   $203.65   $203.60  
  Purchase #4 $91.42   5.665%   $96.5989   $96.60   $96.60   $96.60  
  Purchase #5 $205.44   3.780%   $213.2056   $213.21   $213.20   $213.20  
  Purchase #6 $30.88   7.286%   $33.1299   $33.13   $33.15   $33.10  
  Purchase #7 $169.38   5.128%   $178.0658   $178.07   $178.05   $178.10  
  7 purchase totals = $983.88       $1,041.1564   $1,041.17   $1,041.15   $1,041.20