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 $211.93   3.661%   $219.6888   $219.69   $219.70   $219.70  
  Purchase #2 $196.95   5.782%   $208.3376   $208.34   $208.35   $208.30  
  Purchase #3 $202.69   7.565%   $218.0235   $218.02   $218.00   $218.00  
  Purchase #4 $239.54   5.647%   $253.0668   $253.07   $253.05   $253.10  
  Purchase #5 $244.63   6.754%   $261.1523   $261.15   $261.15   $261.20  
  Purchase #6 $167.82   9.192%   $183.246   $183.25   $183.25   $183.20  
  Purchase #7 $195.29   6.836%   $208.64   $208.64   $208.65   $208.60  
  7 purchase totals = $1,458.85       $1,552.1550   $1,552.16   $1,552.15   $1,552.10