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 $82.46   13.771%   $93.8156   $93.82   $93.80   $93.80  
  Purchase #2 $103.54   10.661%   $114.5784   $114.58   $114.60   $114.60  
  Purchase #3 $52.34   10.759%   $57.9713   $57.97   $57.95   $58.00  
  Purchase #4 $42.68   10.540%   $47.1785   $47.18   $47.20   $47.20  
  Purchase #5 $43.27   12.262%   $48.5758   $48.58   $48.60   $48.60  
  Purchase #6 $61.45   7.339%   $65.9598   $65.96   $65.95   $66.00  
  Purchase #7 $151.77   12.351%   $170.5151   $170.52   $170.50   $170.50  
  7 purchase totals = $537.51       $598.5945   $598.61   $598.60   $598.70