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 $23.44   7.506%   $25.1994   $25.20   $25.20   $25.20  
  Purchase #2 $171.69   13.592%   $195.0261   $195.03   $195.05   $195.00  
  Purchase #3 $10.89   7.228%   $11.6771   $11.68   $11.70   $11.70  
  Purchase #4 $48.36   10.261%   $53.3222   $53.32   $53.30   $53.30  
  Purchase #5 $162.61   12.721%   $183.2956   $183.30   $183.30   $183.30  
  Purchase #6 $208.85   4.576%   $218.407   $218.41   $218.40   $218.40  
  Purchase #7 $231.25   11.193%   $257.1338   $257.13   $257.15   $257.10  
  7 purchase totals = $857.09       $944.0612   $944.07   $944.10   $944.00