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 $41.93   3.122%   $43.2391   $43.24   $43.25   $43.20  
  Purchase #2 $208.35   5.847%   $220.5322   $220.53   $220.55   $220.50  
  Purchase #3 $238.41   11.440%   $265.6841   $265.68   $265.70   $265.70  
  Purchase #4 $93.31   11.774%   $104.2963   $104.30   $104.30   $104.30  
  Purchase #5 $121.93   3.663%   $126.3963   $126.40   $126.40   $126.40  
  Purchase #6 $14.43   8.195%   $15.6125   $15.61   $15.60   $15.60  
  Purchase #7 $26.57   4.163%   $27.6761   $27.68   $27.70   $27.70  
  7 purchase totals = $744.93       $803.4366   $803.44   $803.50   $803.40