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 $242.56   8.232%   $262.5275   $262.53   $262.55   $262.50  
  Purchase #2 $52.81   6.204%   $56.0863   $56.09   $56.10   $56.10  
  Purchase #3 $77.54   6.691%   $82.7282   $82.73   $82.75   $82.70  
  Purchase #4 $50.35   13.825%   $57.3109   $57.31   $57.30   $57.30  
  Purchase #5 $92.59   3.310%   $95.6547   $95.65   $95.65   $95.70  
  Purchase #6 $21.27   11.616%   $23.7407   $23.74   $23.75   $23.70  
  Purchase #7 $53.71   8.459%   $58.2533   $58.25   $58.25   $58.30  
  7 purchase totals = $590.83       $636.3016   $636.30   $636.35   $636.30