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 $245.82   10.675%   $272.0613   $272.06   $272.05   $272.10  
  Purchase #2 $105.27   13.807%   $119.8046   $119.80   $119.80   $119.80  
  Purchase #3 $127.77   6.714%   $136.3485   $136.35   $136.35   $136.30  
  Purchase #4 $114.44   6.795%   $122.2162   $122.22   $122.20   $122.20  
  Purchase #5 $59.44   6.707%   $63.4266   $63.43   $63.45   $63.40  
  Purchase #6 $148.28   4.188%   $154.49   $154.49   $154.50   $154.50  
  Purchase #7 $182.29   7.565%   $196.0802   $196.08   $196.10   $196.10  
  7 purchase totals = $983.31       $1,064.4274   $1,064.43   $1,064.45   $1,064.40