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 $160.39   10.391%   $177.0561   $177.06   $177.05   $177.10  
  Purchase #2 $62.79   9.295%   $68.6263   $68.63   $68.65   $68.60  
  Purchase #3 $201.30   5.783%   $212.9412   $212.94   $212.95   $212.90  
  Purchase #4 $229.81   7.424%   $246.8711   $246.87   $246.85   $246.90  
  Purchase #5 $54.59   12.602%   $61.4694   $61.47   $61.45   $61.50  
  Purchase #6 $124.46   12.684%   $140.2465   $140.25   $140.25   $140.20  
  Purchase #7 $40.27   9.856%   $44.239   $44.24   $44.25   $44.20  
  7 purchase totals = $873.61       $951.4496   $951.46   $951.45   $951.40