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 $106.25   8.421%   $115.1973   $115.20   $115.20   $115.20  
  Purchase #2 $53.85   4.424%   $56.2323   $56.23   $56.25   $56.20  
  Purchase #3 $194.74   6.631%   $207.6532   $207.65   $207.65   $207.70  
  Purchase #4 $69.26   12.438%   $77.8746   $77.87   $77.85   $77.90  
  Purchase #5 $59.63   7.203%   $63.9251   $63.93   $63.95   $63.90  
  Purchase #6 $180.67   8.757%   $196.4913   $196.49   $196.50   $196.50  
  Purchase #7 $194.93   3.432%   $201.62   $201.62   $201.60   $201.60  
  7 purchase totals = $859.33       $918.9938   $918.99   $919.00   $919.00