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 $56.42   7.820%   $60.832   $60.83   $60.85   $60.80  
  Purchase #2 $5.46   6.603%   $5.8205   $5.82   $5.80   $5.80  
  Purchase #3 $222.54   8.523%   $241.5071   $241.51   $241.50   $241.50  
  Purchase #4 $91.54   7.800%   $98.6801   $98.68   $98.70   $98.70  
  Purchase #5 $84.69   5.534%   $89.3767   $89.38   $89.40   $89.40  
  Purchase #6 $127.72   6.140%   $135.562   $135.56   $135.55   $135.60  
  Purchase #7 $187.66   10.688%   $207.7171   $207.72   $207.70   $207.70  
  7 purchase totals = $776.03       $839.4955   $839.50   $839.50   $839.50