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 $216.55   4.343%   $225.9548   $225.95   $225.95   $226.00  
  Purchase #2 $106.99   8.235%   $115.8006   $115.80   $115.80   $115.80  
  Purchase #3 $147.88   10.869%   $163.9531   $163.95   $163.95   $164.00  
  Purchase #4 $24.30   11.718%   $27.1475   $27.15   $27.15   $27.10  
  Purchase #5 $63.94   4.460%   $66.7917   $66.79   $66.80   $66.80  
  Purchase #6 $24.82   4.737%   $25.9957   $26.00   $26.00   $26.00  
  Purchase #7 $197.32   3.410%   $204.0486   $204.05   $204.05   $204.00  
  7 purchase totals = $781.80       $829.6920   $829.69   $829.70   $829.70