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 $67.62   13.284%   $76.6026   $76.60   $76.60   $76.60  
  Purchase #2 $101.88   6.543%   $108.546   $108.55   $108.55   $108.50  
  Purchase #3 $18.66   12.283%   $20.952   $20.95   $20.95   $21.00  
  Purchase #4 $10.45   11.691%   $11.6717   $11.67   $11.65   $11.70  
  Purchase #5 $239.70   3.487%   $248.0583   $248.06   $248.05   $248.10  
  Purchase #6 $22.40   5.484%   $23.6284   $23.63   $23.65   $23.60  
  Purchase #7 $204.50   9.238%   $223.3917   $223.39   $223.40   $223.40  
  7 purchase totals = $665.21       $712.8507   $712.85   $712.85   $712.90