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 $55.96   5.838%   $59.2269   $59.23   $59.25   $59.20  
  Purchase #2 $216.58   10.794%   $239.9576   $239.96   $239.95   $240.00  
  Purchase #3 $6.32   4.460%   $6.6019   $6.60   $6.60   $6.60  
  Purchase #4 $150.27   7.724%   $161.8769   $161.88   $161.90   $161.90  
  Purchase #5 $41.61   8.775%   $45.2613   $45.26   $45.25   $45.30  
  Purchase #6 $23.41   12.773%   $26.4002   $26.40   $26.40   $26.40  
  Purchase #7 $142.41   9.511%   $155.9546   $155.95   $155.95   $156.00  
  7 purchase totals = $636.56       $695.2794   $695.28   $695.30   $695.40