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 $56.49   12.556%   $63.5829   $63.58   $63.60   $63.60  
  Purchase #2 $231.74   3.842%   $240.6435   $240.64   $240.65   $240.60  
  Purchase #3 $211.26   7.472%   $227.0453   $227.05   $227.05   $227.00  
  Purchase #4 $187.89   3.365%   $194.2125   $194.21   $194.20   $194.20  
  Purchase #5 $171.93   11.810%   $192.2349   $192.23   $192.25   $192.20  
  Purchase #6 $141.67   13.794%   $161.212   $161.21   $161.20   $161.20  
  Purchase #7 $186.76   5.116%   $196.3146   $196.31   $196.30   $196.30  
  7 purchase totals = $1,187.74       $1,275.2457   $1,275.23   $1,275.25   $1,275.10