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 $242.38   4.764%   $253.927   $253.93   $253.95   $253.90  
  Purchase #2 $29.45   12.224%   $33.05   $33.05   $33.05   $33.10  
  Purchase #3 $187.35   7.612%   $201.6111   $201.61   $201.60   $201.60  
  Purchase #4 $195.88   6.317%   $208.2537   $208.25   $208.25   $208.30  
  Purchase #5 $194.64   11.209%   $216.4572   $216.46   $216.45   $216.50  
  Purchase #6 $213.49   10.434%   $235.7655   $235.77   $235.75   $235.80  
  Purchase #7 $116.31   8.736%   $126.4708   $126.47   $126.45   $126.50  
  7 purchase totals = $1,179.50       $1,275.5353   $1,275.54   $1,275.50   $1,275.70