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 $41.58   6.164%   $44.143   $44.14   $44.15   $44.10  
  Purchase #2 $123.37   3.239%   $127.366   $127.37   $127.35   $127.40  
  Purchase #3 $178.77   7.403%   $192.0043   $192.00   $192.00   $192.00  
  Purchase #4 $122.88   11.247%   $136.7003   $136.70   $136.70   $136.70  
  Purchase #5 $67.80   9.532%   $74.2627   $74.26   $74.25   $74.30  
  Purchase #6 $127.48   9.479%   $139.5638   $139.56   $139.55   $139.60  
  Purchase #7 $215.70   5.109%   $226.7201   $226.72   $226.70   $226.70  
  7 purchase totals = $877.58       $940.7602   $940.75   $940.70   $940.80