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 $124.26   12.147%   $139.3539   $139.35   $139.35   $139.40  
  Purchase #2 $218.78   6.606%   $233.2326   $233.23   $233.25   $233.20  
  Purchase #3 $27.73   4.604%   $29.0067   $29.01   $29.00   $29.00  
  Purchase #4 $152.43   7.126%   $163.2922   $163.29   $163.30   $163.30  
  Purchase #5 $7.94   6.576%   $8.4621   $8.46   $8.45   $8.50  
  Purchase #6 $232.42   12.277%   $260.9542   $260.95   $260.95   $261.00  
  Purchase #7 $21.90   9.554%   $23.9923   $23.99   $24.00   $24.00  
  7 purchase totals = $785.46       $858.2940   $858.28   $858.30   $858.40