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 $119.63   6.131%   $126.9645   $126.96   $126.95   $127.00  
  Purchase #2 $17.90   6.355%   $19.0375   $19.04   $19.05   $19.00  
  Purchase #3 $183.73   13.151%   $207.8923   $207.89   $207.90   $207.90  
  Purchase #4 $5.40   6.444%   $5.748   $5.75   $5.75   $5.70  
  Purchase #5 $221.60   3.858%   $230.1493   $230.15   $230.15   $230.10  
  Purchase #6 $201.89   10.139%   $222.3596   $222.36   $222.35   $222.40  
  Purchase #7 $186.61   11.661%   $208.3706   $208.37   $208.35   $208.40  
  7 purchase totals = $936.76       $1,020.5218   $1,020.52   $1,020.50   $1,020.50