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 $57.93   4.653%   $60.6255   $60.63   $60.65   $60.60  
  Purchase #2 $237.95   10.821%   $263.6986   $263.70   $263.70   $263.70  
  Purchase #3 $112.50   4.253%   $117.2846   $117.28   $117.30   $117.30  
  Purchase #4 $102.53   11.551%   $114.3732   $114.37   $114.35   $114.40  
  Purchase #5 $115.27   6.727%   $123.0242   $123.02   $123.00   $123.00  
  Purchase #6 $186.92   12.427%   $210.1485   $210.15   $210.15   $210.10  
  Purchase #7 $74.43   12.160%   $83.4807   $83.48   $83.50   $83.50  
  7 purchase totals = $887.53       $972.6353   $972.63   $972.65   $972.60