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 $33.39   8.770%   $36.3183   $36.32   $36.30   $36.30  
  Purchase #2 $228.81   3.139%   $235.9923   $235.99   $236.00   $236.00  
  Purchase #3 $147.29   9.497%   $161.2781   $161.28   $161.30   $161.30  
  Purchase #4 $116.79   7.818%   $125.9206   $125.92   $125.90   $125.90  
  Purchase #5 $191.67   6.179%   $203.5133   $203.51   $203.50   $203.50  
  Purchase #6 $243.63   7.629%   $262.2165   $262.22   $262.20   $262.20  
  Purchase #7 $179.63   7.267%   $192.6837   $192.68   $192.70   $192.70  
  7 purchase totals = $1,141.21       $1,217.9228   $1,217.92   $1,217.90   $1,217.90