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 $227.71   11.812%   $254.6071   $254.61   $254.60   $254.60  
  Purchase #2 $196.82   12.692%   $221.8004   $221.80   $221.80   $221.80  
  Purchase #3 $148.68   8.847%   $161.8337   $161.83   $161.85   $161.80  
  Purchase #4 $207.62   7.556%   $223.3078   $223.31   $223.30   $223.30  
  Purchase #5 $167.68   10.432%   $185.1724   $185.17   $185.15   $185.20  
  Purchase #6 $118.63   5.342%   $124.9672   $124.97   $124.95   $125.00  
  Purchase #7 $116.45   9.813%   $127.8772   $127.88   $127.90   $127.90  
  7 purchase totals = $1,183.59       $1,299.5658   $1,299.57   $1,299.55   $1,299.60