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 $123.92   13.823%   $141.0495   $141.05   $141.05   $141.00  
  Purchase #2 $63.99   9.837%   $70.2847   $70.28   $70.30   $70.30  
  Purchase #3 $237.96   8.628%   $258.4912   $258.49   $258.50   $258.50  
  Purchase #4 $237.42   7.410%   $255.0128   $255.01   $255.00   $255.00  
  Purchase #5 $221.91   9.326%   $242.6053   $242.61   $242.60   $242.60  
  Purchase #6 $69.45   3.654%   $71.9877   $71.99   $72.00   $72.00  
  Purchase #7 $106.94   10.147%   $117.7912   $117.79   $117.80   $117.80  
  7 purchase totals = $1,061.59       $1,157.2224   $1,157.22   $1,157.25   $1,157.20