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 $222.84   6.433%   $237.1753   $237.18   $237.20   $237.20  
  Purchase #2 $56.83   3.218%   $58.6588   $58.66   $58.65   $58.70  
  Purchase #3 $27.96   12.500%   $31.455   $31.46   $31.45   $31.50  
  Purchase #4 $68.85   8.463%   $74.6768   $74.68   $74.70   $74.70  
  Purchase #5 $230.48   6.260%   $244.908   $244.91   $244.90   $244.90  
  Purchase #6 $51.53   5.521%   $54.375   $54.38   $54.40   $54.40  
  Purchase #7 $185.74   8.440%   $201.4165   $201.42   $201.40   $201.40  
  7 purchase totals = $844.23       $902.6654   $902.69   $902.70   $902.80