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 $201.26   3.644%   $208.5939   $208.59   $208.60   $208.60  
  Purchase #2 $170.64   10.197%   $188.0402   $188.04   $188.05   $188.00  
  Purchase #3 $246.43   7.414%   $264.7003   $264.70   $264.70   $264.70  
  Purchase #4 $171.76   7.615%   $184.8395   $184.84   $184.85   $184.80  
  Purchase #5 $232.84   12.793%   $262.6272   $262.63   $262.65   $262.60  
  Purchase #6 $88.25   6.689%   $94.153   $94.15   $94.15   $94.20  
  Purchase #7 $229.34   8.754%   $249.4164   $249.42   $249.40   $249.40  
  7 purchase totals = $1,340.52       $1,452.3705   $1,452.37   $1,452.40   $1,452.30