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 $225.79   12.608%   $254.2576   $254.26   $254.25   $254.30  
  Purchase #2 $159.29   12.147%   $178.639   $178.64   $178.65   $178.60  
  Purchase #3 $163.52   12.737%   $184.3475   $184.35   $184.35   $184.30  
  Purchase #4 $250.74   4.370%   $261.6973   $261.70   $261.70   $261.70  
  Purchase #5 $214.59   7.181%   $229.9997   $230.00   $230.00   $230.00  
  Purchase #6 $103.28   4.141%   $107.5568   $107.56   $107.55   $107.60  
  Purchase #7 $123.49   3.380%   $127.664   $127.66   $127.65   $127.70  
  7 purchase totals = $1,240.70       $1,344.1619   $1,344.17   $1,344.15   $1,344.20