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 $54.67   7.749%   $58.9064   $58.91   $58.90   $58.90  
  Purchase #2 $75.96   10.860%   $84.2093   $84.21   $84.20   $84.20  
  Purchase #3 $33.81   13.147%   $38.255   $38.26   $38.25   $38.30  
  Purchase #4 $123.36   6.145%   $130.9405   $130.94   $130.95   $130.90  
  Purchase #5 $54.43   9.157%   $59.4142   $59.41   $59.40   $59.40  
  Purchase #6 $122.44   10.388%   $135.1591   $135.16   $135.15   $135.20  
  Purchase #7 $136.65   7.135%   $146.4   $146.40   $146.40   $146.40  
  7 purchase totals = $601.32       $653.2845   $653.29   $653.25   $653.30