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 $119.45   4.272%   $124.5529   $124.55   $124.55   $124.60  
  Purchase #2 $17.33   4.693%   $18.1433   $18.14   $18.15   $18.10  
  Purchase #3 $199.93   3.359%   $206.6456   $206.65   $206.65   $206.60  
  Purchase #4 $148.65   9.677%   $163.0349   $163.03   $163.05   $163.00  
  Purchase #5 $119.88   6.820%   $128.0558   $128.06   $128.05   $128.10  
  Purchase #6 $229.55   13.805%   $261.2394   $261.24   $261.25   $261.20  
  Purchase #7 $147.32   7.842%   $158.8728   $158.87   $158.85   $158.90  
  7 purchase totals = $982.11       $1,060.5447   $1,060.54   $1,060.55   $1,060.50