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 $158.93   10.600%   $175.7766   $175.78   $175.80   $175.80  
  Purchase #2 $46.46   7.411%   $49.9032   $49.90   $49.90   $49.90  
  Purchase #3 $33.90   6.548%   $36.1198   $36.12   $36.10   $36.10  
  Purchase #4 $92.95   5.250%   $97.8299   $97.83   $97.85   $97.80  
  Purchase #5 $127.68   3.581%   $132.2522   $132.25   $132.25   $132.30  
  Purchase #6 $233.25   5.747%   $246.6549   $246.65   $246.65   $246.70  
  Purchase #7 $103.51   13.243%   $117.2178   $117.22   $117.20   $117.20  
  7 purchase totals = $796.68       $855.7544   $855.75   $855.75   $855.80