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 $56.41   6.269%   $59.9463   $59.95   $59.95   $59.90  
  Purchase #2 $110.85   9.106%   $120.944   $120.94   $120.95   $120.90  
  Purchase #3 $9.88   7.564%   $10.6273   $10.63   $10.65   $10.60  
  Purchase #4 $78.27   6.263%   $83.1721   $83.17   $83.15   $83.20  
  Purchase #5 $236.98   13.793%   $269.6667   $269.67   $269.65   $269.70  
  Purchase #6 $69.54   12.304%   $78.0962   $78.10   $78.10   $78.10  
  Purchase #7 $30.74   10.664%   $34.0181   $34.02   $34.00   $34.00  
  7 purchase totals = $592.67       $656.4707   $656.48   $656.45   $656.40