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 $86.53   8.176%   $93.6047   $93.60   $93.60   $93.60  
  Purchase #2 $22.69   3.593%   $23.5053   $23.51   $23.50   $23.50  
  Purchase #3 $89.60   11.801%   $100.1737   $100.17   $100.15   $100.20  
  Purchase #4 $70.98   10.539%   $78.4606   $78.46   $78.45   $78.50  
  Purchase #5 $196.43   5.204%   $206.6522   $206.65   $206.65   $206.70  
  Purchase #6 $101.62   6.565%   $108.2914   $108.29   $108.30   $108.30  
  Purchase #7 $217.36   11.512%   $242.3825   $242.38   $242.40   $242.40  
  7 purchase totals = $785.21       $853.0704   $853.06   $853.05   $853.20