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 $52.52   11.455%   $58.5362   $58.54   $58.55   $58.50  
  Purchase #2 $235.99   10.166%   $259.9807   $259.98   $260.00   $260.00  
  Purchase #3 $24.72   7.759%   $26.638   $26.64   $26.65   $26.60  
  Purchase #4 $75.72   6.493%   $80.6365   $80.64   $80.65   $80.60  
  Purchase #5 $217.30   9.211%   $237.3155   $237.32   $237.30   $237.30  
  Purchase #6 $98.59   13.501%   $111.9006   $111.90   $111.90   $111.90  
  Purchase #7 $31.39   11.744%   $35.0764   $35.08   $35.10   $35.10  
  7 purchase totals = $736.23       $810.0839   $810.10   $810.15   $810.00