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 $92.59   10.634%   $102.436   $102.44   $102.45   $102.40  
  Purchase #2 $225.81   13.443%   $256.1656   $256.17   $256.15   $256.20  
  Purchase #3 $71.47   4.458%   $74.6561   $74.66   $74.65   $74.70  
  Purchase #4 $228.31   5.648%   $241.2049   $241.20   $241.20   $241.20  
  Purchase #5 $95.66   12.565%   $107.6797   $107.68   $107.70   $107.70  
  Purchase #6 $103.37   6.132%   $109.7086   $109.71   $109.70   $109.70  
  Purchase #7 $144.77   10.583%   $160.091   $160.09   $160.10   $160.10  
  7 purchase totals = $961.98       $1,051.9419   $1,051.95   $1,051.95   $1,052.00