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 $111.98   8.610%   $121.6215   $121.62   $121.60   $121.60  
  Purchase #2 $70.94   3.187%   $73.2009   $73.20   $73.20   $73.20  
  Purchase #3 $89.25   7.567%   $96.0035   $96.00   $96.00   $96.00  
  Purchase #4 $107.92   5.831%   $114.2128   $114.21   $114.20   $114.20  
  Purchase #5 $74.31   3.666%   $77.0342   $77.03   $77.05   $77.00  
  Purchase #6 $49.62   10.583%   $54.8713   $54.87   $54.85   $54.90  
  Purchase #7 $215.27   9.620%   $235.979   $235.98   $236.00   $236.00  
  7 purchase totals = $719.29       $772.9232   $772.91   $772.90   $772.90