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 $246.91   5.814%   $261.2653   $261.27   $261.25   $261.30  
  Purchase #2 $179.95   6.483%   $191.6162   $191.62   $191.60   $191.60  
  Purchase #3 $104.29   9.317%   $114.0067   $114.01   $114.00   $114.00  
  Purchase #4 $197.40   13.295%   $223.6443   $223.64   $223.65   $223.60  
  Purchase #5 $118.47   4.225%   $123.4754   $123.48   $123.50   $123.50  
  Purchase #6 $9.39   5.755%   $9.9304   $9.93   $9.95   $9.90  
  Purchase #7 $121.68   11.129%   $135.2218   $135.22   $135.20   $135.20  
  7 purchase totals = $978.09       $1,059.1601   $1,059.17   $1,059.15   $1,059.10