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 $38.66   13.795%   $43.9931   $43.99   $44.00   $44.00  
  Purchase #2 $238.53   12.360%   $268.0123   $268.01   $268.00   $268.00  
  Purchase #3 $161.37   3.269%   $166.6452   $166.65   $166.65   $166.60  
  Purchase #4 $135.66   12.241%   $152.2661   $152.27   $152.25   $152.30  
  Purchase #5 $8.69   9.107%   $9.4814   $9.48   $9.50   $9.50  
  Purchase #6 $209.26   12.750%   $235.9407   $235.94   $235.95   $235.90  
  Purchase #7 $35.96   10.704%   $39.8092   $39.81   $39.80   $39.80  
  7 purchase totals = $828.13       $916.1480   $916.15   $916.15   $916.10