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 $69.52   13.150%   $78.6619   $78.66   $78.65   $78.70  
  Purchase #2 $146.33   8.427%   $158.6612   $158.66   $158.65   $158.70  
  Purchase #3 $10.99   4.640%   $11.4999   $11.50   $11.50   $11.50  
  Purchase #4 $105.65   11.709%   $118.0206   $118.02   $118.00   $118.00  
  Purchase #5 $133.75   4.148%   $139.298   $139.30   $139.30   $139.30  
  Purchase #6 $195.26   9.619%   $214.0421   $214.04   $214.05   $214.00  
  Purchase #7 $163.41   7.704%   $175.9991   $176.00   $176.00   $176.00  
  7 purchase totals = $824.91       $896.1828   $896.18   $896.15   $896.20