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 $76.58   9.683%   $83.9952   $84.00   $84.00   $84.00  
  Purchase #2 $186.55   3.795%   $193.6296   $193.63   $193.65   $193.60  
  Purchase #3 $79.71   5.107%   $83.7808   $83.78   $83.80   $83.80  
  Purchase #4 $96.94   3.854%   $100.6761   $100.68   $100.70   $100.70  
  Purchase #5 $127.69   6.748%   $136.3065   $136.31   $136.30   $136.30  
  Purchase #6 $102.88   8.653%   $111.7822   $111.78   $111.80   $111.80  
  Purchase #7 $20.54   10.409%   $22.678   $22.68   $22.70   $22.70  
  7 purchase totals = $690.89       $732.8484   $732.86   $732.95   $732.90