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 $96.77   6.454%   $103.0155   $103.02   $103.00   $103.00  
  Purchase #2 $79.89   12.696%   $90.0328   $90.03   $90.05   $90.00  
  Purchase #3 $201.46   10.821%   $223.26   $223.26   $223.25   $223.30  
  Purchase #4 $178.76   11.701%   $199.6767   $199.68   $199.70   $199.70  
  Purchase #5 $48.47   7.626%   $52.1663   $52.17   $52.15   $52.20  
  Purchase #6 $120.96   3.716%   $125.4549   $125.45   $125.45   $125.50  
  Purchase #7 $190.38   10.623%   $210.6041   $210.60   $210.60   $210.60  
  7 purchase totals = $916.69       $1,004.2103   $1,004.21   $1,004.20   $1,004.30