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 $63.79   4.852%   $66.8851   $66.89   $66.90   $66.90  
  Purchase #2 $77.92   4.183%   $81.1794   $81.18   $81.20   $81.20  
  Purchase #3 $96.80   4.405%   $101.064   $101.06   $101.05   $101.10  
  Purchase #4 $167.53   12.561%   $188.5734   $188.57   $188.55   $188.60  
  Purchase #5 $80.68   7.624%   $86.831   $86.83   $86.85   $86.80  
  Purchase #6 $22.79   7.749%   $24.556   $24.56   $24.55   $24.60  
  Purchase #7 $140.51   10.611%   $155.4195   $155.42   $155.40   $155.40  
  7 purchase totals = $650.02       $704.5084   $704.51   $704.50   $704.60