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 $106.70   11.724%   $119.2095   $119.21   $119.20   $119.20  
  Purchase #2 $16.75   9.584%   $18.3553   $18.36   $18.35   $18.40  
  Purchase #3 $25.94   3.215%   $26.774   $26.77   $26.75   $26.80  
  Purchase #4 $226.34   12.475%   $254.5759   $254.58   $254.60   $254.60  
  Purchase #5 $95.82   9.758%   $105.1701   $105.17   $105.15   $105.20  
  Purchase #6 $109.46   4.590%   $114.4842   $114.48   $114.50   $114.50  
  Purchase #7 $107.73   13.872%   $122.6743   $122.67   $122.65   $122.70  
  7 purchase totals = $688.74       $761.2433   $761.24   $761.20   $761.40