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 $76.42   8.228%   $82.7078   $82.71   $82.70   $82.70  
  Purchase #2 $149.39   7.225%   $160.1834   $160.18   $160.20   $160.20  
  Purchase #3 $179.61   4.805%   $188.2403   $188.24   $188.25   $188.20  
  Purchase #4 $120.36   12.330%   $135.2004   $135.20   $135.20   $135.20  
  Purchase #5 $235.46   11.724%   $263.0653   $263.07   $263.05   $263.10  
  Purchase #6 $189.44   8.367%   $205.2904   $205.29   $205.30   $205.30  
  Purchase #7 $206.97   10.108%   $227.8905   $227.89   $227.90   $227.90  
  7 purchase totals = $1,157.65       $1,262.5781   $1,262.58   $1,262.60   $1,262.60