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 $236.49   12.365%   $265.732   $265.73   $265.75   $265.70  
  Purchase #2 $248.93   5.796%   $263.358   $263.36   $263.35   $263.40  
  Purchase #3 $218.38   9.197%   $238.4644   $238.46   $238.45   $238.50  
  Purchase #4 $22.77   6.719%   $24.2999   $24.30   $24.30   $24.30  
  Purchase #5 $22.53   3.356%   $23.2861   $23.29   $23.30   $23.30  
  Purchase #6 $56.37   3.683%   $58.4461   $58.45   $58.45   $58.40  
  Purchase #7 $177.92   3.572%   $184.2753   $184.28   $184.30   $184.30  
  7 purchase totals = $983.39       $1,057.8618   $1,057.87   $1,057.90   $1,057.90