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 $246.88   8.279%   $267.3192   $267.32   $267.30   $267.30  
  Purchase #2 $195.60   3.807%   $203.0465   $203.05   $203.05   $203.00  
  Purchase #3 $43.63   12.116%   $48.9162   $48.92   $48.90   $48.90  
  Purchase #4 $70.86   10.348%   $78.1926   $78.19   $78.20   $78.20  
  Purchase #5 $221.98   5.420%   $234.0113   $234.01   $234.00   $234.00  
  Purchase #6 $214.36   9.164%   $234.004   $234.00   $234.00   $234.00  
  Purchase #7 $244.78   10.581%   $270.6802   $270.68   $270.70   $270.70  
  7 purchase totals = $1,238.09       $1,336.1700   $1,336.17   $1,336.15   $1,336.10