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 $70.81   8.631%   $76.9216   $76.92   $76.90   $76.90  
  Purchase #2 $173.84   10.297%   $191.7403   $191.74   $191.75   $191.70  
  Purchase #3 $55.32   5.560%   $58.3958   $58.40   $58.40   $58.40  
  Purchase #4 $200.49   3.776%   $208.0605   $208.06   $208.05   $208.10  
  Purchase #5 $179.96   5.401%   $189.6796   $189.68   $189.70   $189.70  
  Purchase #6 $99.32   9.326%   $108.5826   $108.58   $108.60   $108.60  
  Purchase #7 $21.31   13.364%   $24.1579   $24.16   $24.15   $24.20  
  7 purchase totals = $801.05       $857.5383   $857.54   $857.55   $857.60