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 $114.61   11.243%   $127.4956   $127.50   $127.50   $127.50  
  Purchase #2 $21.45   5.759%   $22.6853   $22.69   $22.70   $22.70  
  Purchase #3 $70.84   6.695%   $75.5827   $75.58   $75.60   $75.60  
  Purchase #4 $180.70   11.714%   $201.8672   $201.87   $201.85   $201.90  
  Purchase #5 $234.92   13.855%   $267.4682   $267.47   $267.45   $267.50  
  Purchase #6 $81.43   5.648%   $86.0292   $86.03   $86.05   $86.00  
  Purchase #7 $15.81   10.771%   $17.5129   $17.51   $17.50   $17.50  
  7 purchase totals = $719.76       $798.6411   $798.65   $798.65   $798.70