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 $176.56   8.768%   $192.0408   $192.04   $192.05   $192.00  
  Purchase #2 $55.55   7.691%   $59.8224   $59.82   $59.80   $59.80  
  Purchase #3 $114.47   7.152%   $122.6569   $122.66   $122.65   $122.70  
  Purchase #4 $187.32   7.128%   $200.6722   $200.67   $200.65   $200.70  
  Purchase #5 $240.96   7.188%   $258.2802   $258.28   $258.30   $258.30  
  Purchase #6 $17.57   9.112%   $19.171   $19.17   $19.15   $19.20  
  Purchase #7 $105.53   9.106%   $115.1396   $115.14   $115.15   $115.10  
  7 purchase totals = $897.96       $967.7831   $967.78   $967.75   $967.80