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 $131.59   6.410%   $140.0249   $140.02   $140.00   $140.00  
  Purchase #2 $191.57   4.401%   $200.001   $200.00   $200.00   $200.00  
  Purchase #3 $138.87   5.328%   $146.269   $146.27   $146.25   $146.30  
  Purchase #4 $184.51   13.490%   $209.4004   $209.40   $209.40   $209.40  
  Purchase #5 $124.77   9.767%   $136.9563   $136.96   $136.95   $137.00  
  Purchase #6 $100.92   12.109%   $113.1404   $113.14   $113.15   $113.10  
  Purchase #7 $240.44   10.423%   $265.5011   $265.50   $265.50   $265.50  
  7 purchase totals = $1,112.67       $1,211.2931   $1,211.29   $1,211.25   $1,211.30