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 $105.30   13.757%   $119.7861   $119.79   $119.80   $119.80  
  Purchase #2 $218.62   6.228%   $232.2357   $232.24   $232.25   $232.20  
  Purchase #3 $54.72   12.508%   $61.5644   $61.56   $61.55   $61.60  
  Purchase #4 $74.68   8.687%   $81.1675   $81.17   $81.15   $81.20  
  Purchase #5 $193.43   7.793%   $208.504   $208.50   $208.50   $208.50  
  Purchase #6 $204.74   4.627%   $214.2133   $214.21   $214.20   $214.20  
  Purchase #7 $74.70   4.523%   $78.0787   $78.08   $78.10   $78.10  
  7 purchase totals = $926.19       $995.5497   $995.55   $995.55   $995.60