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 $52.29   8.569%   $56.7707   $56.77   $56.75   $56.80  
  Purchase #2 $14.74   6.711%   $15.7292   $15.73   $15.75   $15.70  
  Purchase #3 $185.94   3.542%   $192.526   $192.53   $192.55   $192.50  
  Purchase #4 $152.77   12.193%   $171.3972   $171.40   $171.40   $171.40  
  Purchase #5 $213.70   5.363%   $225.1607   $225.16   $225.15   $225.20  
  Purchase #6 $72.69   10.396%   $80.2469   $80.25   $80.25   $80.20  
  Purchase #7 $173.31   11.834%   $193.8195   $193.82   $193.80   $193.80  
  7 purchase totals = $865.44       $935.6502   $935.66   $935.65   $935.60