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 $211.27   10.434%   $233.3139   $233.31   $233.30   $233.30  
  Purchase #2 $173.99   13.407%   $197.3168   $197.32   $197.30   $197.30  
  Purchase #3 $77.60   5.831%   $82.1249   $82.12   $82.10   $82.10  
  Purchase #4 $235.66   6.173%   $250.2073   $250.21   $250.20   $250.20  
  Purchase #5 $149.31   9.298%   $163.1928   $163.19   $163.20   $163.20  
  Purchase #6 $242.75   8.445%   $263.2502   $263.25   $263.25   $263.30  
  Purchase #7 $126.34   8.373%   $136.9184   $136.92   $136.90   $136.90  
  7 purchase totals = $1,216.92       $1,326.3243   $1,326.32   $1,326.25   $1,326.30