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 $118.54   6.698%   $126.4798   $126.48   $126.50   $126.50  
  Purchase #2 $149.31   5.267%   $157.1742   $157.17   $157.15   $157.20  
  Purchase #3 $20.91   12.730%   $23.5718   $23.57   $23.55   $23.60  
  Purchase #4 $44.64   3.274%   $46.1015   $46.10   $46.10   $46.10  
  Purchase #5 $211.43   11.406%   $235.5457   $235.55   $235.55   $235.50  
  Purchase #6 $133.79   8.463%   $145.1126   $145.11   $145.10   $145.10  
  Purchase #7 $123.81   10.645%   $136.9896   $136.99   $137.00   $137.00  
  7 purchase totals = $802.43       $870.9752   $870.97   $870.95   $871.00