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 $53.38   9.804%   $58.6134   $58.61   $58.60   $58.60  
  Purchase #2 $69.49   8.121%   $75.1333   $75.13   $75.15   $75.10  
  Purchase #3 $33.93   12.554%   $38.1896   $38.19   $38.20   $38.20  
  Purchase #4 $111.44   11.789%   $124.5777   $124.58   $124.60   $124.60  
  Purchase #5 $25.92   5.439%   $27.3298   $27.33   $27.35   $27.30  
  Purchase #6 $188.62   11.239%   $209.819   $209.82   $209.80   $209.80  
  Purchase #7 $86.46   13.418%   $98.0612   $98.06   $98.05   $98.10  
  7 purchase totals = $569.24       $631.7240   $631.72   $631.75   $631.70