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 $108.43   10.225%   $119.517   $119.52   $119.50   $119.50  
  Purchase #2 $202.52   3.369%   $209.3429   $209.34   $209.35   $209.30  
  Purchase #3 $214.47   7.768%   $231.13   $231.13   $231.15   $231.10  
  Purchase #4 $242.40   11.822%   $271.0565   $271.06   $271.05   $271.10  
  Purchase #5 $8.43   11.513%   $9.4005   $9.40   $9.40   $9.40  
  Purchase #6 $122.64   11.641%   $136.9165   $136.92   $136.90   $136.90  
  Purchase #7 $93.45   5.594%   $98.6776   $98.68   $98.70   $98.70  
  7 purchase totals = $992.34       $1,076.0410   $1,076.05   $1,076.05   $1,076.00