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 $76.41   10.596%   $84.5064   $84.51   $84.50   $84.50  
  Purchase #2 $241.61   4.724%   $253.0237   $253.02   $253.00   $253.00  
  Purchase #3 $23.47   4.853%   $24.609   $24.61   $24.60   $24.60  
  Purchase #4 $212.65   6.326%   $226.1022   $226.10   $226.10   $226.10  
  Purchase #5 $248.72   4.626%   $260.2258   $260.23   $260.25   $260.20  
  Purchase #6 $80.45   12.750%   $90.7074   $90.71   $90.70   $90.70  
  Purchase #7 $78.83   7.835%   $85.0063   $85.01   $85.00   $85.00  
  7 purchase totals = $962.14       $1,024.1808   $1,024.19   $1,024.15   $1,024.10