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 $119.95   5.226%   $126.2186   $126.22   $126.20   $126.20  
  Purchase #2 $155.25   13.785%   $176.6512   $176.65   $176.65   $176.70  
  Purchase #3 $197.95   3.807%   $205.486   $205.49   $205.50   $205.50  
  Purchase #4 $198.94   7.142%   $213.1483   $213.15   $213.15   $213.10  
  Purchase #5 $98.43   9.115%   $107.4019   $107.40   $107.40   $107.40  
  Purchase #6 $55.26   12.551%   $62.1957   $62.20   $62.20   $62.20  
  Purchase #7 $20.98   10.859%   $23.2582   $23.26   $23.25   $23.30  
  7 purchase totals = $846.76       $914.3599   $914.37   $914.35   $914.40