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 $41.87   5.247%   $44.0669   $44.07   $44.05   $44.10  
  Purchase #2 $244.69   10.703%   $270.8792   $270.88   $270.90   $270.90  
  Purchase #3 $63.45   10.573%   $70.1586   $70.16   $70.15   $70.20  
  Purchase #4 $211.77   5.357%   $223.1145   $223.11   $223.10   $223.10  
  Purchase #5 $241.25   5.592%   $254.7407   $254.74   $254.75   $254.70  
  Purchase #6 $130.93   10.255%   $144.3569   $144.36   $144.35   $144.40  
  Purchase #7 $33.38   6.652%   $35.6004   $35.60   $35.60   $35.60  
  7 purchase totals = $967.34       $1,042.9172   $1,042.92   $1,042.90   $1,043.00