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 $46.90   11.559%   $52.3212   $52.32   $52.30   $52.30  
  Purchase #2 $164.85   13.830%   $187.6488   $187.65   $187.65   $187.60  
  Purchase #3 $110.93   6.105%   $117.7023   $117.70   $117.70   $117.70  
  Purchase #4 $220.60   5.619%   $232.9955   $233.00   $233.00   $233.00  
  Purchase #5 $58.65   5.213%   $61.7074   $61.71   $61.70   $61.70  
  Purchase #6 $43.76   12.167%   $49.0843   $49.08   $49.10   $49.10  
  Purchase #7 $217.33   11.389%   $242.0817   $242.08   $242.10   $242.10  
  7 purchase totals = $863.02       $943.5412   $943.54   $943.55   $943.50