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 $142.81   6.612%   $152.2526   $152.25   $152.25   $152.30  
  Purchase #2 $49.44   13.373%   $56.0516   $56.05   $56.05   $56.10  
  Purchase #3 $150.29   6.807%   $160.5202   $160.52   $160.50   $160.50  
  Purchase #4 $227.81   12.156%   $255.5026   $255.50   $255.50   $255.50  
  Purchase #5 $232.80   8.781%   $253.2422   $253.24   $253.25   $253.20  
  Purchase #6 $69.84   5.423%   $73.6274   $73.63   $73.65   $73.60  
  Purchase #7 $31.59   6.299%   $33.5799   $33.58   $33.60   $33.60  
  7 purchase totals = $904.58       $984.7765   $984.77   $984.80   $984.80