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 $93.64   4.832%   $98.1647   $98.16   $98.15   $98.20  
  Purchase #2 $56.83   12.656%   $64.0224   $64.02   $64.00   $64.00  
  Purchase #3 $96.72   9.688%   $106.0902   $106.09   $106.10   $106.10  
  Purchase #4 $62.85   10.288%   $69.316   $69.32   $69.30   $69.30  
  Purchase #5 $52.40   12.530%   $58.9657   $58.97   $58.95   $59.00  
  Purchase #6 $246.69   6.407%   $262.4954   $262.50   $262.50   $262.50  
  Purchase #7 $241.32   13.386%   $273.6231   $273.62   $273.60   $273.60  
  7 purchase totals = $850.45       $932.6775   $932.68   $932.60   $932.70