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 $83.47   5.529%   $88.0851   $88.09   $88.10   $88.10  
  Purchase #2 $160.61   3.721%   $166.5863   $166.59   $166.60   $166.60  
  Purchase #3 $234.63   8.353%   $254.2286   $254.23   $254.25   $254.20  
  Purchase #4 $23.43   5.508%   $24.7205   $24.72   $24.70   $24.70  
  Purchase #5 $36.99   5.512%   $39.0289   $39.03   $39.05   $39.00  
  Purchase #6 $192.76   5.826%   $203.9902   $203.99   $204.00   $204.00  
  Purchase #7 $227.88   10.141%   $250.9893   $250.99   $251.00   $251.00  
  7 purchase totals = $959.77       $1,027.6289   $1,027.64   $1,027.70   $1,027.60