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 $64.30   5.809%   $68.0352   $68.04   $68.05   $68.00  
  Purchase #2 $235.33   13.299%   $266.6265   $266.63   $266.65   $266.60  
  Purchase #3 $68.51   9.604%   $75.0897   $75.09   $75.10   $75.10  
  Purchase #4 $229.34   8.682%   $249.2513   $249.25   $249.25   $249.30  
  Purchase #5 $53.56   7.168%   $57.3992   $57.40   $57.40   $57.40  
  Purchase #6 $94.46   9.796%   $103.7133   $103.71   $103.70   $103.70  
  Purchase #7 $20.62   11.633%   $23.0187   $23.02   $23.00   $23.00  
  7 purchase totals = $766.12       $843.1339   $843.14   $843.15   $843.10