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 $119.70   12.773%   $134.9893   $134.99   $135.00   $135.00  
  Purchase #2 $77.79   5.863%   $82.3508   $82.35   $82.35   $82.40  
  Purchase #3 $50.54   4.798%   $52.9649   $52.96   $52.95   $53.00  
  Purchase #4 $175.97   8.336%   $190.6389   $190.64   $190.65   $190.60  
  Purchase #5 $151.27   6.373%   $160.9104   $160.91   $160.90   $160.90  
  Purchase #6 $231.60   6.826%   $247.409   $247.41   $247.40   $247.40  
  Purchase #7 $71.42   11.846%   $79.8804   $79.88   $79.90   $79.90  
  7 purchase totals = $878.29       $949.1437   $949.14   $949.15   $949.20