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 $181.50   6.535%   $193.361   $193.36   $193.35   $193.40  
  Purchase #2 $53.98   10.629%   $59.7175   $59.72   $59.70   $59.70  
  Purchase #3 $16.28   7.211%   $17.454   $17.45   $17.45   $17.50  
  Purchase #4 $185.86   4.240%   $193.7405   $193.74   $193.75   $193.70  
  Purchase #5 $229.40   10.247%   $252.9066   $252.91   $252.90   $252.90  
  Purchase #6 $220.41   13.202%   $249.5085   $249.51   $249.50   $249.50  
  Purchase #7 $41.36   9.356%   $45.2296   $45.23   $45.25   $45.20  
  7 purchase totals = $928.79       $1,011.9177   $1,011.92   $1,011.90   $1,011.90