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 $168.61   8.120%   $182.3011   $182.30   $182.30   $182.30  
  Purchase #2 $33.60   5.851%   $35.5659   $35.57   $35.55   $35.60  
  Purchase #3 $247.73   4.531%   $258.9546   $258.95   $258.95   $259.00  
  Purchase #4 $20.72   8.262%   $22.4319   $22.43   $22.45   $22.40  
  Purchase #5 $215.90   8.630%   $234.5322   $234.53   $234.55   $234.50  
  Purchase #6 $200.47   4.172%   $208.8336   $208.83   $208.85   $208.80  
  Purchase #7 $247.29   10.267%   $272.6793   $272.68   $272.70   $272.70  
  7 purchase totals = $1,134.32       $1,215.2986   $1,215.29   $1,215.35   $1,215.30