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 $62.92   11.326%   $70.0463   $70.05   $70.05   $70.00  
  Purchase #2 $228.99   7.801%   $246.8535   $246.85   $246.85   $246.90  
  Purchase #3 $42.58   12.712%   $47.9928   $47.99   $48.00   $48.00  
  Purchase #4 $124.53   7.647%   $134.0528   $134.05   $134.05   $134.10  
  Purchase #5 $61.81   13.575%   $70.2007   $70.20   $70.20   $70.20  
  Purchase #6 $56.92   5.755%   $60.1957   $60.20   $60.20   $60.20  
  Purchase #7 $121.84   11.214%   $135.5031   $135.50   $135.50   $135.50  
  7 purchase totals = $699.59       $764.8449   $764.84   $764.85   $764.90