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 $62.25   4.514%   $65.06   $65.06   $65.05   $65.10  
  Purchase #2 $17.83   3.351%   $18.4275   $18.43   $18.45   $18.40  
  Purchase #3 $203.86   11.759%   $227.8319   $227.83   $227.85   $227.80  
  Purchase #4 $191.76   12.780%   $216.2669   $216.27   $216.25   $216.30  
  Purchase #5 $201.36   6.627%   $214.7041   $214.70   $214.70   $214.70  
  Purchase #6 $146.26   7.387%   $157.0642   $157.06   $157.05   $157.10  
  Purchase #7 $119.41   4.673%   $124.99   $124.99   $125.00   $125.00  
  7 purchase totals = $942.73       $1,024.3446   $1,024.34   $1,024.35   $1,024.40