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 $236.74   10.691%   $262.0499   $262.05   $262.05   $262.00  
  Purchase #2 $44.97   12.722%   $50.6911   $50.69   $50.70   $50.70  
  Purchase #3 $208.37   13.782%   $237.0876   $237.09   $237.10   $237.10  
  Purchase #4 $193.34   5.814%   $204.5808   $204.58   $204.60   $204.60  
  Purchase #5 $249.32   8.664%   $270.9211   $270.92   $270.90   $270.90  
  Purchase #6 $87.82   7.863%   $94.7253   $94.73   $94.75   $94.70  
  Purchase #7 $120.53   11.799%   $134.7513   $134.75   $134.75   $134.80  
  7 purchase totals = $1,141.09       $1,254.8071   $1,254.81   $1,254.85   $1,254.80