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 $155.82   7.592%   $167.6499   $167.65   $167.65   $167.60  
  Purchase #2 $50.31   11.420%   $56.0554   $56.06   $56.05   $56.10  
  Purchase #3 $152.34   13.358%   $172.6896   $172.69   $172.70   $172.70  
  Purchase #4 $58.87   8.196%   $63.695   $63.70   $63.70   $63.70  
  Purchase #5 $234.80   4.236%   $244.7461   $244.75   $244.75   $244.70  
  Purchase #6 $146.55   7.760%   $157.9223   $157.92   $157.90   $157.90  
  Purchase #7 $7.40   11.466%   $8.2485   $8.25   $8.25   $8.20  
  7 purchase totals = $806.09       $871.0068   $871.02   $871.00   $870.90