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 $59.76   8.260%   $64.6962   $64.70   $64.70   $64.70  
  Purchase #2 $199.83   11.238%   $222.2869   $222.29   $222.30   $222.30  
  Purchase #3 $228.74   3.423%   $236.5698   $236.57   $236.55   $236.60  
  Purchase #4 $180.89   7.138%   $193.8019   $193.80   $193.80   $193.80  
  Purchase #5 $242.56   13.642%   $275.65   $275.65   $275.65   $275.70  
  Purchase #6 $31.26   11.215%   $34.7658   $34.77   $34.75   $34.80  
  Purchase #7 $223.49   12.204%   $250.7647   $250.76   $250.75   $250.80  
  7 purchase totals = $1,166.53       $1,278.5353   $1,278.54   $1,278.50   $1,278.70