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 $147.59   6.702%   $157.4815   $157.48   $157.50   $157.50  
  Purchase #2 $250.93   6.694%   $267.7273   $267.73   $267.75   $267.70  
  Purchase #3 $42.79   3.241%   $44.1768   $44.18   $44.20   $44.20  
  Purchase #4 $93.69   10.455%   $103.4853   $103.49   $103.50   $103.50  
  Purchase #5 $248.42   9.488%   $271.9901   $271.99   $272.00   $272.00  
  Purchase #6 $52.82   4.312%   $55.0976   $55.10   $55.10   $55.10  
  Purchase #7 $69.48   10.222%   $76.5822   $76.58   $76.60   $76.60  
  7 purchase totals = $905.72       $976.5408   $976.55   $976.65   $976.60