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 $241.27   9.284%   $263.6695   $263.67   $263.65   $263.70  
  Purchase #2 $158.91   13.772%   $180.7951   $180.80   $180.80   $180.80  
  Purchase #3 $67.31   13.277%   $76.2467   $76.25   $76.25   $76.20  
  Purchase #4 $69.88   9.358%   $76.4194   $76.42   $76.40   $76.40  
  Purchase #5 $168.77   3.731%   $175.0668   $175.07   $175.05   $175.10  
  Purchase #6 $5.63   8.721%   $6.121   $6.12   $6.10   $6.10  
  Purchase #7 $188.82   7.828%   $203.6008   $203.60   $203.60   $203.60  
  7 purchase totals = $900.59       $981.9193   $981.93   $981.85   $981.90