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 $213.34   8.813%   $232.1417   $232.14   $232.15   $232.10  
  Purchase #2 $138.99   5.728%   $146.9513   $146.95   $146.95   $147.00  
  Purchase #3 $225.27   4.620%   $235.6775   $235.68   $235.70   $235.70  
  Purchase #4 $210.25   8.860%   $228.8782   $228.88   $228.90   $228.90  
  Purchase #5 $53.66   12.379%   $60.3026   $60.30   $60.30   $60.30  
  Purchase #6 $57.49   12.156%   $64.4785   $64.48   $64.50   $64.50  
  Purchase #7 $164.87   5.194%   $173.4333   $173.43   $173.45   $173.40  
  7 purchase totals = $1,063.87       $1,141.8631   $1,141.86   $1,141.95   $1,141.90