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 $52.29   8.200%   $56.5778   $56.58   $56.60   $56.60  
  Purchase #2 $137.57   3.540%   $142.44   $142.44   $142.45   $142.40  
  Purchase #3 $135.88   13.544%   $154.2836   $154.28   $154.30   $154.30  
  Purchase #4 $118.79   4.761%   $124.4456   $124.45   $124.45   $124.40  
  Purchase #5 $69.53   11.432%   $77.4787   $77.48   $77.50   $77.50  
  Purchase #6 $210.49   8.863%   $229.1457   $229.15   $229.15   $229.10  
  Purchase #7 $214.35   6.115%   $227.4575   $227.46   $227.45   $227.50  
  7 purchase totals = $938.90       $1,011.8289   $1,011.84   $1,011.90   $1,011.80