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 $55.58   11.487%   $61.9645   $61.96   $61.95   $62.00  
  Purchase #2 $93.65   10.298%   $103.2941   $103.29   $103.30   $103.30  
  Purchase #3 $243.46   7.301%   $261.235   $261.24   $261.25   $261.20  
  Purchase #4 $227.56   3.257%   $234.9716   $234.97   $234.95   $235.00  
  Purchase #5 $58.29   3.278%   $60.2007   $60.20   $60.20   $60.20  
  Purchase #6 $154.64   12.673%   $174.2375   $174.24   $174.25   $174.20  
  Purchase #7 $105.89   4.112%   $110.2442   $110.24   $110.25   $110.20  
  7 purchase totals = $939.07       $1,006.1476   $1,006.14   $1,006.15   $1,006.10