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 $58.46   9.338%   $63.919   $63.92   $63.90   $63.90  
  Purchase #2 $187.86   7.748%   $202.4154   $202.42   $202.40   $202.40  
  Purchase #3 $207.45   13.113%   $234.6529   $234.65   $234.65   $234.70  
  Purchase #4 $131.82   11.564%   $147.0637   $147.06   $147.05   $147.10  
  Purchase #5 $38.67   11.577%   $43.1468   $43.15   $43.15   $43.10  
  Purchase #6 $228.30   13.395%   $258.8808   $258.88   $258.90   $258.90  
  Purchase #7 $71.68   7.503%   $77.0582   $77.06   $77.05   $77.10  
  7 purchase totals = $924.24       $1,027.1368   $1,027.14   $1,027.10   $1,027.20