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 $184.91   4.846%   $193.8707   $193.87   $193.85   $193.90  
  Purchase #2 $88.80   5.158%   $93.3803   $93.38   $93.40   $93.40  
  Purchase #3 $217.39   11.322%   $242.0029   $242.00   $242.00   $242.00  
  Purchase #4 $162.67   6.139%   $172.6563   $172.66   $172.65   $172.70  
  Purchase #5 $223.28   11.706%   $249.4172   $249.42   $249.40   $249.40  
  Purchase #6 $196.70   5.741%   $207.9925   $207.99   $208.00   $208.00  
  Purchase #7 $175.87   12.764%   $198.318   $198.32   $198.30   $198.30  
  7 purchase totals = $1,249.62       $1,357.6379   $1,357.64   $1,357.60   $1,357.70