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 $58.74   4.256%   $61.24   $61.24   $61.25   $61.20  
  Purchase #2 $44.37   7.714%   $47.7927   $47.79   $47.80   $47.80  
  Purchase #3 $61.34   3.741%   $63.6347   $63.63   $63.65   $63.60  
  Purchase #4 $136.55   10.706%   $151.169   $151.17   $151.15   $151.20  
  Purchase #5 $200.76   13.752%   $228.3685   $228.37   $228.35   $228.40  
  Purchase #6 $57.30   7.324%   $61.4967   $61.50   $61.50   $61.50  
  Purchase #7 $74.96   4.604%   $78.4112   $78.41   $78.40   $78.40  
  7 purchase totals = $634.02       $692.1128   $692.11   $692.10   $692.10