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 $32.85   13.327%   $37.2279   $37.23   $37.25   $37.20  
  Purchase #2 $60.65   7.641%   $65.2843   $65.28   $65.30   $65.30  
  Purchase #3 $99.49   6.279%   $105.737   $105.74   $105.75   $105.70  
  Purchase #4 $144.42   6.873%   $154.346   $154.35   $154.35   $154.30  
  Purchase #5 $246.49   6.201%   $261.7748   $261.77   $261.75   $261.80  
  Purchase #6 $186.93   5.648%   $197.4878   $197.49   $197.50   $197.50  
  Purchase #7 $109.49   11.449%   $122.0255   $122.03   $122.05   $122.00  
  7 purchase totals = $880.32       $943.8833   $943.89   $943.95   $943.80