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 $183.92   7.795%   $198.2566   $198.26   $198.25   $198.30  
  Purchase #2 $15.86   13.850%   $18.0566   $18.06   $18.05   $18.10  
  Purchase #3 $86.82   8.178%   $93.9201   $93.92   $93.90   $93.90  
  Purchase #4 $93.91   10.323%   $103.6043   $103.60   $103.60   $103.60  
  Purchase #5 $223.57   3.140%   $230.5901   $230.59   $230.60   $230.60  
  Purchase #6 $36.42   4.425%   $38.0316   $38.03   $38.05   $38.00  
  Purchase #7 $245.27   6.811%   $261.9753   $261.98   $262.00   $262.00  
  7 purchase totals = $885.77       $944.4346   $944.44   $944.45   $944.50