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 $234.67   11.545%   $261.7627   $261.76   $261.75   $261.80  
  Purchase #2 $63.89   6.475%   $68.0269   $68.03   $68.05   $68.00  
  Purchase #3 $33.91   9.574%   $37.1565   $37.16   $37.15   $37.20  
  Purchase #4 $31.25   9.741%   $34.2941   $34.29   $34.30   $34.30  
  Purchase #5 $44.76   9.476%   $49.0015   $49.00   $49.00   $49.00  
  Purchase #6 $211.69   12.586%   $238.3333   $238.33   $238.35   $238.30  
  Purchase #7 $212.79   5.423%   $224.3296   $224.33   $224.35   $224.30  
  7 purchase totals = $832.96       $912.9046   $912.90   $912.95   $912.90