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 $219.79   11.620%   $245.3296   $245.33   $245.35   $245.30  
  Purchase #2 $15.94   10.290%   $17.5802   $17.58   $17.60   $17.60  
  Purchase #3 $50.97   13.388%   $57.7939   $57.79   $57.80   $57.80  
  Purchase #4 $36.49   10.409%   $40.2882   $40.29   $40.30   $40.30  
  Purchase #5 $111.71   9.291%   $122.089   $122.09   $122.10   $122.10  
  Purchase #6 $218.76   5.725%   $231.284   $231.28   $231.30   $231.30  
  Purchase #7 $247.70   9.639%   $271.5758   $271.58   $271.60   $271.60  
  7 purchase totals = $901.36       $985.9407   $985.94   $986.05   $986.00