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 $65.76   11.314%   $73.2001   $73.20   $73.20   $73.20  
  Purchase #2 $172.60   8.480%   $187.2365   $187.24   $187.25   $187.20  
  Purchase #3 $22.79   5.590%   $24.064   $24.06   $24.05   $24.10  
  Purchase #4 $125.98   10.870%   $139.674   $139.67   $139.65   $139.70  
  Purchase #5 $248.81   8.200%   $269.2124   $269.21   $269.20   $269.20  
  Purchase #6 $200.92   4.785%   $210.534   $210.53   $210.55   $210.50  
  Purchase #7 $27.43   9.662%   $30.0803   $30.08   $30.10   $30.10  
  7 purchase totals = $864.29       $934.0013   $933.99   $934.00   $934.00