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 $248.26   4.729%   $260.0002   $260.00   $260.00   $260.00  
  Purchase #2 $22.25   6.751%   $23.7521   $23.75   $23.75   $23.80  
  Purchase #3 $93.80   11.461%   $104.5504   $104.55   $104.55   $104.60  
  Purchase #4 $96.74   9.340%   $105.7755   $105.78   $105.80   $105.80  
  Purchase #5 $122.53   11.476%   $136.5915   $136.59   $136.60   $136.60  
  Purchase #6 $226.94   7.484%   $243.9242   $243.92   $243.90   $243.90  
  Purchase #7 $42.52   13.126%   $48.1012   $48.10   $48.10   $48.10  
  7 purchase totals = $853.04       $922.6951   $922.69   $922.70   $922.80