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 $176.58   12.508%   $198.6666   $198.67   $198.65   $198.70  
  Purchase #2 $26.44   3.726%   $27.4252   $27.43   $27.45   $27.40  
  Purchase #3 $102.64   4.378%   $107.1336   $107.13   $107.15   $107.10  
  Purchase #4 $76.29   10.856%   $84.572   $84.57   $84.55   $84.60  
  Purchase #5 $166.48   8.359%   $180.3961   $180.40   $180.40   $180.40  
  Purchase #6 $92.30   5.736%   $97.5943   $97.59   $97.60   $97.60  
  Purchase #7 $111.79   4.853%   $117.2152   $117.22   $117.20   $117.20  
  7 purchase totals = $752.52       $813.0030   $813.01   $813.00   $813.00