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 $182.52   9.593%   $200.0291   $200.03   $200.05   $200.00  
  Purchase #2 $26.46   8.283%   $28.6517   $28.65   $28.65   $28.70  
  Purchase #3 $228.30   8.798%   $248.3858   $248.39   $248.40   $248.40  
  Purchase #4 $225.89   5.329%   $237.9277   $237.93   $237.95   $237.90  
  Purchase #5 $42.27   6.691%   $45.0983   $45.10   $45.10   $45.10  
  Purchase #6 $45.93   6.594%   $48.9586   $48.96   $48.95   $49.00  
  Purchase #7 $239.50   11.497%   $267.0353   $267.04   $267.05   $267.00  
  7 purchase totals = $990.87       $1,076.0865   $1,076.10   $1,076.15   $1,076.10