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 $64.29   4.164%   $66.967   $66.97   $66.95   $67.00  
  Purchase #2 $102.42   9.163%   $111.8047   $111.80   $111.80   $111.80  
  Purchase #3 $111.68   11.739%   $124.7901   $124.79   $124.80   $124.80  
  Purchase #4 $160.89   3.717%   $166.8703   $166.87   $166.85   $166.90  
  Purchase #5 $132.73   4.419%   $138.5953   $138.60   $138.60   $138.60  
  Purchase #6 $137.99   4.457%   $144.1402   $144.14   $144.15   $144.10  
  Purchase #7 $234.93   7.724%   $253.076   $253.08   $253.10   $253.10  
  7 purchase totals = $944.93       $1,006.2436   $1,006.25   $1,006.25   $1,006.30