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 $102.64   11.114%   $114.0474   $114.05   $114.05   $114.00  
  Purchase #2 $35.42   9.749%   $38.8731   $38.87   $38.85   $38.90  
  Purchase #3 $77.91   13.712%   $88.593   $88.59   $88.60   $88.60  
  Purchase #4 $171.52   9.754%   $188.2501   $188.25   $188.25   $188.30  
  Purchase #5 $246.87   10.405%   $272.5568   $272.56   $272.55   $272.60  
  Purchase #6 $69.63   13.473%   $79.0112   $79.01   $79.00   $79.00  
  Purchase #7 $179.33   11.629%   $200.1843   $200.18   $200.20   $200.20  
  7 purchase totals = $883.32       $981.5159   $981.51   $981.50   $981.60