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 $242.58   8.720%   $263.733   $263.73   $263.75   $263.70  
  Purchase #2 $111.34   12.656%   $125.4312   $125.43   $125.45   $125.40  
  Purchase #3 $99.40   4.583%   $103.9555   $103.96   $103.95   $104.00  
  Purchase #4 $184.77   6.575%   $196.9186   $196.92   $196.90   $196.90  
  Purchase #5 $70.76   6.635%   $75.4549   $75.45   $75.45   $75.50  
  Purchase #6 $26.97   3.501%   $27.9142   $27.91   $27.90   $27.90  
  Purchase #7 $197.28   10.613%   $218.2173   $218.22   $218.20   $218.20  
  7 purchase totals = $933.10       $1,011.6247   $1,011.62   $1,011.60   $1,011.60