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 $234.54   7.447%   $252.0062   $252.01   $252.00   $252.00  
  Purchase #2 $163.47   5.488%   $172.4412   $172.44   $172.45   $172.40  
  Purchase #3 $73.50   4.848%   $77.0633   $77.06   $77.05   $77.10  
  Purchase #4 $250.92   6.512%   $267.2599   $267.26   $267.25   $267.30  
  Purchase #5 $77.84   6.625%   $82.9969   $83.00   $83.00   $83.00  
  Purchase #6 $129.54   4.677%   $135.5986   $135.60   $135.60   $135.60  
  Purchase #7 $78.92   8.617%   $85.7205   $85.72   $85.70   $85.70  
  7 purchase totals = $1,008.73       $1,073.0866   $1,073.09   $1,073.05   $1,073.10