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 $62.55   5.593%   $66.0484   $66.05   $66.05   $66.00  
  Purchase #2 $216.87   8.407%   $235.1023   $235.10   $235.10   $235.10  
  Purchase #3 $236.50   10.842%   $262.1413   $262.14   $262.15   $262.10  
  Purchase #4 $77.96   10.523%   $86.1637   $86.16   $86.15   $86.20  
  Purchase #5 $27.77   9.308%   $30.3548   $30.35   $30.35   $30.40  
  Purchase #6 $127.93   12.478%   $143.8931   $143.89   $143.90   $143.90  
  Purchase #7 $183.62   4.494%   $191.8719   $191.87   $191.85   $191.90  
  7 purchase totals = $933.20       $1,015.5755   $1,015.56   $1,015.55   $1,015.60