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 $50.77   11.194%   $56.4532   $56.45   $56.45   $56.50  
  Purchase #2 $109.63   13.306%   $124.2174   $124.22   $124.20   $124.20  
  Purchase #3 $119.70   13.183%   $135.4801   $135.48   $135.50   $135.50  
  Purchase #4 $191.67   3.423%   $198.2309   $198.23   $198.25   $198.20  
  Purchase #5 $246.77   12.421%   $277.4213   $277.42   $277.40   $277.40  
  Purchase #6 $126.49   6.179%   $134.3058   $134.31   $134.30   $134.30  
  Purchase #7 $235.91   13.739%   $268.3217   $268.32   $268.30   $268.30  
  7 purchase totals = $1,080.94       $1,194.4304   $1,194.43   $1,194.40   $1,194.40