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 $163.37   8.795%   $177.7384   $177.74   $177.75   $177.70  
  Purchase #2 $207.92   12.636%   $234.1928   $234.19   $234.20   $234.20  
  Purchase #3 $159.60   9.364%   $174.5449   $174.54   $174.55   $174.50  
  Purchase #4 $45.38   7.858%   $48.946   $48.95   $48.95   $48.90  
  Purchase #5 $33.44   13.715%   $38.0263   $38.03   $38.05   $38.00  
  Purchase #6 $195.96   13.592%   $222.5949   $222.59   $222.60   $222.60  
  Purchase #7 $164.60   9.862%   $180.8329   $180.83   $180.85   $180.80  
  7 purchase totals = $970.27       $1,076.8762   $1,076.87   $1,076.95   $1,076.70