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 $139.28   11.473%   $155.2596   $155.26   $155.25   $155.30  
  Purchase #2 $106.79   6.194%   $113.4046   $113.40   $113.40   $113.40  
  Purchase #3 $89.26   6.444%   $95.0119   $95.01   $95.00   $95.00  
  Purchase #4 $233.97   10.123%   $257.6548   $257.65   $257.65   $257.70  
  Purchase #5 $219.73   3.502%   $227.4249   $227.42   $227.40   $227.40  
  Purchase #6 $47.44   5.183%   $49.8988   $49.90   $49.90   $49.90  
  Purchase #7 $130.81   10.383%   $144.392   $144.39   $144.40   $144.40  
  7 purchase totals = $967.28       $1,043.0466   $1,043.03   $1,043.00   $1,043.10