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 $68.25   4.816%   $71.5369   $71.54   $71.55   $71.50  
  Purchase #2 $94.44   10.369%   $104.2325   $104.23   $104.25   $104.20  
  Purchase #3 $156.50   3.115%   $161.375   $161.38   $161.40   $161.40  
  Purchase #4 $36.87   4.430%   $38.5033   $38.50   $38.50   $38.50  
  Purchase #5 $48.49   11.355%   $53.996   $54.00   $54.00   $54.00  
  Purchase #6 $135.72   8.256%   $146.925   $146.93   $146.95   $146.90  
  Purchase #7 $178.51   6.808%   $190.663   $190.66   $190.65   $190.70  
  7 purchase totals = $718.78       $767.2317   $767.24   $767.30   $767.20