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 $239.84   11.651%   $267.7838   $267.78   $267.80   $267.80  
  Purchase #2 $135.36   6.840%   $144.6186   $144.62   $144.60   $144.60  
  Purchase #3 $170.49   12.602%   $191.9751   $191.98   $192.00   $192.00  
  Purchase #4 $216.77   6.311%   $230.4504   $230.45   $230.45   $230.50  
  Purchase #5 $42.94   4.234%   $44.7581   $44.76   $44.75   $44.80  
  Purchase #6 $8.47   12.527%   $9.531   $9.53   $9.55   $9.50  
  Purchase #7 $173.61   8.505%   $188.3755   $188.38   $188.40   $188.40  
  7 purchase totals = $987.48       $1,077.4925   $1,077.50   $1,077.55   $1,077.60