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 $233.66   13.578%   $265.3864   $265.39   $265.40   $265.40  
  Purchase #2 $177.85   9.834%   $195.3398   $195.34   $195.35   $195.30  
  Purchase #3 $63.89   12.273%   $71.7312   $71.73   $71.75   $71.70  
  Purchase #4 $32.69   6.262%   $34.737   $34.74   $34.75   $34.70  
  Purchase #5 $217.28   11.143%   $241.4915   $241.49   $241.50   $241.50  
  Purchase #6 $8.45   4.255%   $8.8095   $8.81   $8.80   $8.80  
  Purchase #7 $126.94   7.192%   $136.0695   $136.07   $136.05   $136.10  
  7 purchase totals = $860.76       $953.5649   $953.57   $953.60   $953.50