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 $75.83   10.255%   $83.6064   $83.61   $83.60   $83.60  
  Purchase #2 $110.25   13.241%   $124.8482   $124.85   $124.85   $124.80  
  Purchase #3 $62.96   4.150%   $65.5728   $65.57   $65.55   $65.60  
  Purchase #4 $221.90   8.759%   $241.3362   $241.34   $241.35   $241.30  
  Purchase #5 $245.38   12.724%   $276.6022   $276.60   $276.60   $276.60  
  Purchase #6 $52.56   6.737%   $56.101   $56.10   $56.10   $56.10  
  Purchase #7 $27.76   11.625%   $30.9871   $30.99   $31.00   $31.00  
  7 purchase totals = $796.64       $879.0539   $879.06   $879.05   $879.00