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 $200.76   5.534%   $211.8701   $211.87   $211.85   $211.90  
  Purchase #2 $53.26   5.469%   $56.1728   $56.17   $56.15   $56.20  
  Purchase #3 $61.88   3.666%   $64.1485   $64.15   $64.15   $64.10  
  Purchase #4 $198.86   8.494%   $215.7512   $215.75   $215.75   $215.80  
  Purchase #5 $40.58   5.129%   $42.6613   $42.66   $42.65   $42.70  
  Purchase #6 $64.99   7.753%   $70.0287   $70.03   $70.05   $70.00  
  Purchase #7 $170.26   12.779%   $192.0175   $192.02   $192.00   $192.00  
  7 purchase totals = $790.59       $852.6501   $852.65   $852.60   $852.70