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 $90.49   6.337%   $96.2244   $96.22   $96.20   $96.20  
  Purchase #2 $65.46   6.394%   $69.6455   $69.65   $69.65   $69.60  
  Purchase #3 $104.57   8.252%   $113.1991   $113.20   $113.20   $113.20  
  Purchase #4 $23.27   12.648%   $26.2132   $26.21   $26.20   $26.20  
  Purchase #5 $243.45   9.558%   $266.719   $266.72   $266.70   $266.70  
  Purchase #6 $237.57   5.377%   $250.3441   $250.34   $250.35   $250.30  
  Purchase #7 $193.46   6.847%   $206.7062   $206.71   $206.70   $206.70  
  7 purchase totals = $958.27       $1,029.0515   $1,029.05   $1,029.00   $1,028.90