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 $47.62   12.755%   $53.6939   $53.69   $53.70   $53.70  
  Purchase #2 $179.35   13.241%   $203.0977   $203.10   $203.10   $203.10  
  Purchase #3 $236.58   10.501%   $261.4233   $261.42   $261.40   $261.40  
  Purchase #4 $73.30   9.807%   $80.4885   $80.49   $80.50   $80.50  
  Purchase #5 $195.81   7.452%   $210.4018   $210.40   $210.40   $210.40  
  Purchase #6 $231.74   4.118%   $241.2831   $241.28   $241.30   $241.30  
  Purchase #7 $228.79   10.678%   $253.2202   $253.22   $253.20   $253.20  
  7 purchase totals = $1,193.19       $1,303.6085   $1,303.60   $1,303.60   $1,303.60