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 $207.40   4.863%   $217.4859   $217.49   $217.50   $217.50  
  Purchase #2 $219.91   3.795%   $228.2556   $228.26   $228.25   $228.30  
  Purchase #3 $120.43   12.720%   $135.7487   $135.75   $135.75   $135.70  
  Purchase #4 $221.47   12.450%   $249.043   $249.04   $249.05   $249.00  
  Purchase #5 $53.62   12.663%   $60.4099   $60.41   $60.40   $60.40  
  Purchase #6 $111.70   8.386%   $121.0672   $121.07   $121.05   $121.10  
  Purchase #7 $121.48   10.301%   $133.9937   $133.99   $134.00   $134.00  
  7 purchase totals = $1,056.01       $1,146.0040   $1,146.01   $1,146.00   $1,146.00