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 $50.47   13.446%   $57.2562   $57.26   $57.25   $57.30  
  Purchase #2 $97.71   5.243%   $102.8329   $102.83   $102.85   $102.80  
  Purchase #3 $205.46   5.739%   $217.2513   $217.25   $217.25   $217.30  
  Purchase #4 $242.69   11.229%   $269.9417   $269.94   $269.95   $269.90  
  Purchase #5 $240.55   5.560%   $253.9246   $253.92   $253.90   $253.90  
  Purchase #6 $74.74   10.651%   $82.7006   $82.70   $82.70   $82.70  
  Purchase #7 $86.75   5.248%   $91.3026   $91.30   $91.30   $91.30  
  7 purchase totals = $998.37       $1,075.2099   $1,075.20   $1,075.20   $1,075.20