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 $243.34   8.279%   $263.4861   $263.49   $263.50   $263.50  
  Purchase #2 $213.65   9.102%   $233.0964   $233.10   $233.10   $233.10  
  Purchase #3 $55.77   12.247%   $62.6002   $62.60   $62.60   $62.60  
  Purchase #4 $250.68   8.160%   $271.1355   $271.14   $271.15   $271.10  
  Purchase #5 $124.72   9.644%   $136.748   $136.75   $136.75   $136.70  
  Purchase #6 $57.58   10.717%   $63.7508   $63.75   $63.75   $63.80  
  Purchase #7 $23.62   11.163%   $26.2567   $26.26   $26.25   $26.30  
  7 purchase totals = $969.36       $1,057.0737   $1,057.09   $1,057.10   $1,057.10