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 $131.76   3.713%   $136.6522   $136.65   $136.65   $136.70  
  Purchase #2 $49.38   4.399%   $51.5522   $51.55   $51.55   $51.60  
  Purchase #3 $110.70   8.402%   $120.001   $120.00   $120.00   $120.00  
  Purchase #4 $235.64   13.116%   $266.5465   $266.55   $266.55   $266.50  
  Purchase #5 $6.82   3.475%   $7.057   $7.06   $7.05   $7.10  
  Purchase #6 $74.63   4.332%   $77.863   $77.86   $77.85   $77.90  
  Purchase #7 $90.78   5.756%   $96.0053   $96.01   $96.00   $96.00  
  7 purchase totals = $699.71       $755.6772   $755.68   $755.65   $755.80