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 $51.68   11.630%   $57.6904   $57.69   $57.70   $57.70  
  Purchase #2 $211.45   6.382%   $224.9447   $224.94   $224.95   $224.90  
  Purchase #3 $23.75   3.442%   $24.5675   $24.57   $24.55   $24.60  
  Purchase #4 $32.85   3.586%   $34.028   $34.03   $34.05   $34.00  
  Purchase #5 $122.26   4.498%   $127.7593   $127.76   $127.75   $127.80  
  Purchase #6 $151.77   6.768%   $162.0418   $162.04   $162.05   $162.00  
  Purchase #7 $162.47   13.344%   $184.15   $184.15   $184.15   $184.20  
  7 purchase totals = $756.23       $815.1817   $815.18   $815.20   $815.20