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 $33.58   3.349%   $34.7046   $34.70   $34.70   $34.70  
  Purchase #2 $190.44   8.702%   $207.0121   $207.01   $207.00   $207.00  
  Purchase #3 $141.49   7.129%   $151.5768   $151.58   $151.60   $151.60  
  Purchase #4 $86.78   7.583%   $93.3605   $93.36   $93.35   $93.40  
  Purchase #5 $58.34   9.158%   $63.6828   $63.68   $63.70   $63.70  
  Purchase #6 $113.29   12.252%   $127.1703   $127.17   $127.15   $127.20  
  Purchase #7 $147.45   5.856%   $156.0847   $156.08   $156.10   $156.10  
  7 purchase totals = $771.37       $833.5918   $833.58   $833.60   $833.70