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 $25.98   13.679%   $29.5338   $29.53   $29.55   $29.50  
  Purchase #2 $44.94   3.621%   $46.5673   $46.57   $46.55   $46.60  
  Purchase #3 $139.76   10.440%   $154.3509   $154.35   $154.35   $154.40  
  Purchase #4 $25.91   6.342%   $27.5532   $27.55   $27.55   $27.60  
  Purchase #5 $163.80   9.311%   $179.0514   $179.05   $179.05   $179.10  
  Purchase #6 $241.68   8.674%   $262.6433   $262.64   $262.65   $262.60  
  Purchase #7 $69.80   9.415%   $76.3717   $76.37   $76.35   $76.40  
  7 purchase totals = $711.87       $776.0716   $776.06   $776.05   $776.20