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 $195.82   5.175%   $205.9537   $205.95   $205.95   $206.00  
  Purchase #2 $108.97   4.357%   $113.7178   $113.72   $113.70   $113.70  
  Purchase #3 $109.72   11.320%   $122.1403   $122.14   $122.15   $122.10  
  Purchase #4 $74.27   11.184%   $82.5764   $82.58   $82.60   $82.60  
  Purchase #5 $31.94   5.720%   $33.767   $33.77   $33.75   $33.80  
  Purchase #6 $155.54   4.144%   $161.9856   $161.99   $162.00   $162.00  
  Purchase #7 $127.51   12.672%   $143.6681   $143.67   $143.65   $143.70  
  7 purchase totals = $803.77       $863.8089   $863.82   $863.80   $863.90