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 $214.97   12.336%   $241.4887   $241.49   $241.50   $241.50  
  Purchase #2 $248.97   13.554%   $282.7154   $282.72   $282.70   $282.70  
  Purchase #3 $151.36   10.138%   $166.7049   $166.70   $166.70   $166.70  
  Purchase #4 $44.53   3.506%   $46.0912   $46.09   $46.10   $46.10  
  Purchase #5 $77.81   4.418%   $81.2476   $81.25   $81.25   $81.20  
  Purchase #6 $16.29   12.467%   $18.3209   $18.32   $18.30   $18.30  
  Purchase #7 $166.82   13.491%   $189.3257   $189.33   $189.35   $189.30  
  7 purchase totals = $920.75       $1,025.8944   $1,025.90   $1,025.90   $1,025.80