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 $105.41   5.322%   $111.0199   $111.02   $111.00   $111.00  
  Purchase #2 $209.77   11.841%   $234.6089   $234.61   $234.60   $234.60  
  Purchase #3 $26.39   12.235%   $29.6188   $29.62   $29.60   $29.60  
  Purchase #4 $228.36   12.641%   $257.227   $257.23   $257.25   $257.20  
  Purchase #5 $124.93   9.562%   $136.8758   $136.88   $136.90   $136.90  
  Purchase #6 $211.71   8.233%   $229.1401   $229.14   $229.15   $229.10  
  Purchase #7 $13.45   12.641%   $15.1502   $15.15   $15.15   $15.20  
  7 purchase totals = $920.02       $1,013.6407   $1,013.65   $1,013.65   $1,013.60