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 $214.65   5.441%   $226.3291   $226.33   $226.35   $226.30  
  Purchase #2 $32.74   12.570%   $36.8554   $36.86   $36.85   $36.90  
  Purchase #3 $11.26   6.292%   $11.9685   $11.97   $11.95   $12.00  
  Purchase #4 $78.95   4.643%   $82.6156   $82.62   $82.60   $82.60  
  Purchase #5 $172.69   3.114%   $178.0676   $178.07   $178.05   $178.10  
  Purchase #6 $223.94   11.632%   $249.9887   $249.99   $250.00   $250.00  
  Purchase #7 $11.86   13.650%   $13.4789   $13.48   $13.50   $13.50  
  7 purchase totals = $746.09       $799.3038   $799.32   $799.30   $799.40