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 $125.72   12.786%   $141.7946   $141.79   $141.80   $141.80  
  Purchase #2 $73.27   4.462%   $76.5393   $76.54   $76.55   $76.50  
  Purchase #3 $106.68   7.363%   $114.5348   $114.53   $114.55   $114.50  
  Purchase #4 $181.77   8.698%   $197.5804   $197.58   $197.60   $197.60  
  Purchase #5 $32.74   5.815%   $34.6438   $34.64   $34.65   $34.60  
  Purchase #6 $204.83   3.287%   $211.5628   $211.56   $211.55   $211.60  
  Purchase #7 $89.73   12.331%   $100.7946   $100.79   $100.80   $100.80  
  7 purchase totals = $814.74       $877.4503   $877.43   $877.50   $877.40