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 $248.26   5.140%   $261.0206   $261.02   $261.00   $261.00  
  Purchase #2 $205.35   6.167%   $218.0139   $218.01   $218.00   $218.00  
  Purchase #3 $7.77   7.672%   $8.3661   $8.37   $8.35   $8.40  
  Purchase #4 $215.81   5.851%   $228.437   $228.44   $228.45   $228.40  
  Purchase #5 $184.95   13.699%   $210.2863   $210.29   $210.30   $210.30  
  Purchase #6 $49.61   12.818%   $55.969   $55.97   $55.95   $56.00  
  Purchase #7 $169.59   9.506%   $185.7112   $185.71   $185.70   $185.70  
  7 purchase totals = $1,081.34       $1,167.8041   $1,167.81   $1,167.75   $1,167.80