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 $205.98   10.382%   $227.3648   $227.36   $227.35   $227.40  
  Purchase #2 $161.39   9.460%   $176.6575   $176.66   $176.65   $176.70  
  Purchase #3 $170.94   5.432%   $180.2255   $180.23   $180.25   $180.20  
  Purchase #4 $53.31   8.218%   $57.691   $57.69   $57.70   $57.70  
  Purchase #5 $231.41   8.281%   $250.5731   $250.57   $250.55   $250.60  
  Purchase #6 $154.90   3.502%   $160.3246   $160.32   $160.30   $160.30  
  Purchase #7 $10.97   13.468%   $12.4474   $12.45   $12.45   $12.40  
  7 purchase totals = $988.90       $1,065.2839   $1,065.28   $1,065.25   $1,065.30