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 $248.48   11.549%   $277.177   $277.18   $277.20   $277.20  
  Purchase #2 $53.49   13.357%   $60.6347   $60.63   $60.65   $60.60  
  Purchase #3 $192.87   8.855%   $209.9486   $209.95   $209.95   $209.90  
  Purchase #4 $229.34   12.482%   $257.9662   $257.97   $257.95   $258.00  
  Purchase #5 $127.31   5.270%   $134.0192   $134.02   $134.00   $134.00  
  Purchase #6 $173.57   5.201%   $182.5974   $182.60   $182.60   $182.60  
  Purchase #7 $46.31   11.502%   $51.6366   $51.64   $51.65   $51.60  
  7 purchase totals = $1,071.37       $1,173.9797   $1,173.99   $1,174.00   $1,173.90