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 $62.57   10.558%   $69.1761   $69.18   $69.20   $69.20  
  Purchase #2 $122.59   11.259%   $136.3924   $136.39   $136.40   $136.40  
  Purchase #3 $235.56   13.286%   $266.8565   $266.86   $266.85   $266.90  
  Purchase #4 $59.71   5.305%   $62.8776   $62.88   $62.90   $62.90  
  Purchase #5 $163.58   13.129%   $185.0564   $185.06   $185.05   $185.10  
  Purchase #6 $201.96   13.721%   $229.6709   $229.67   $229.65   $229.70  
  Purchase #7 $118.83   8.142%   $128.5051   $128.51   $128.50   $128.50  
  7 purchase totals = $964.80       $1,078.5350   $1,078.55   $1,078.55   $1,078.70