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 $106.32   11.755%   $118.8179   $118.82   $118.80   $118.80  
  Purchase #2 $227.87   13.662%   $259.0016   $259.00   $259.00   $259.00  
  Purchase #3 $167.48   11.529%   $186.7888   $186.79   $186.80   $186.80  
  Purchase #4 $46.71   8.497%   $50.6789   $50.68   $50.70   $50.70  
  Purchase #5 $122.63   6.152%   $130.1742   $130.17   $130.15   $130.20  
  Purchase #6 $250.28   11.327%   $278.6292   $278.63   $278.65   $278.60  
  Purchase #7 $165.40   3.790%   $171.6687   $171.67   $171.65   $171.70  
  7 purchase totals = $1,086.69       $1,195.7593   $1,195.76   $1,195.75   $1,195.80