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 $24.55   3.755%   $25.4719   $25.47   $25.45   $25.50  
  Purchase #2 $240.99   3.295%   $248.9306   $248.93   $248.95   $248.90  
  Purchase #3 $77.26   9.393%   $84.517   $84.52   $84.50   $84.50  
  Purchase #4 $235.98   9.608%   $258.653   $258.65   $258.65   $258.70  
  Purchase #5 $58.43   8.239%   $63.244   $63.24   $63.25   $63.20  
  Purchase #6 $179.34   9.851%   $197.0068   $197.01   $197.00   $197.00  
  Purchase #7 $153.61   3.531%   $159.034   $159.03   $159.05   $159.00  
  7 purchase totals = $970.16       $1,036.8573   $1,036.85   $1,036.85   $1,036.80