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 $48.55   9.295%   $53.0627   $53.06   $53.05   $53.10  
  Purchase #2 $190.54   5.260%   $200.5624   $200.56   $200.55   $200.60  
  Purchase #3 $164.66   3.647%   $170.6652   $170.67   $170.65   $170.70  
  Purchase #4 $28.59   5.627%   $30.1988   $30.20   $30.20   $30.20  
  Purchase #5 $73.47   12.397%   $82.5781   $82.58   $82.60   $82.60  
  Purchase #6 $202.88   3.602%   $210.1877   $210.19   $210.20   $210.20  
  Purchase #7 $11.74   12.343%   $13.1891   $13.19   $13.20   $13.20  
  7 purchase totals = $720.43       $760.4440   $760.45   $760.45   $760.60