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 $240.78   11.543%   $268.5732   $268.57   $268.55   $268.60  
  Purchase #2 $94.36   3.112%   $97.2965   $97.30   $97.30   $97.30  
  Purchase #3 $49.64   4.136%   $51.6931   $51.69   $51.70   $51.70  
  Purchase #4 $147.40   5.396%   $155.3537   $155.35   $155.35   $155.40  
  Purchase #5 $80.91   6.166%   $85.8989   $85.90   $85.90   $85.90  
  Purchase #6 $53.61   5.663%   $56.6459   $56.65   $56.65   $56.60  
  Purchase #7 $237.33   12.153%   $266.1727   $266.17   $266.15   $266.20  
  7 purchase totals = $904.03       $981.6340   $981.63   $981.60   $981.70