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 $76.83   8.274%   $83.1869   $83.19   $83.20   $83.20  
  Purchase #2 $230.87   3.528%   $239.0151   $239.02   $239.00   $239.00  
  Purchase #3 $45.49   11.278%   $50.6204   $50.62   $50.60   $50.60  
  Purchase #4 $87.91   3.678%   $91.1433   $91.14   $91.15   $91.10  
  Purchase #5 $56.73   11.302%   $63.1416   $63.14   $63.15   $63.10  
  Purchase #6 $154.76   8.275%   $167.5664   $167.57   $167.55   $167.60  
  Purchase #7 $60.85   4.467%   $63.5682   $63.57   $63.55   $63.60  
  7 purchase totals = $713.44       $758.2419   $758.25   $758.20   $758.20