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 $154.83   8.837%   $168.5123   $168.51   $168.50   $168.50  
  Purchase #2 $69.88   8.158%   $75.5808   $75.58   $75.60   $75.60  
  Purchase #3 $51.26   4.490%   $53.5616   $53.56   $53.55   $53.60  
  Purchase #4 $163.81   5.544%   $172.8916   $172.89   $172.90   $172.90  
  Purchase #5 $158.92   7.429%   $170.7262   $170.73   $170.75   $170.70  
  Purchase #6 $54.47   13.725%   $61.946   $61.95   $61.95   $61.90  
  Purchase #7 $224.43   11.488%   $250.2125   $250.21   $250.20   $250.20  
  7 purchase totals = $877.60       $953.4310   $953.43   $953.45   $953.40