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 $243.29   10.223%   $268.1615   $268.16   $268.15   $268.20  
  Purchase #2 $39.67   12.719%   $44.7156   $44.72   $44.70   $44.70  
  Purchase #3 $187.95   4.622%   $196.637   $196.64   $196.65   $196.60  
  Purchase #4 $153.32   5.591%   $161.8921   $161.89   $161.90   $161.90  
  Purchase #5 $181.96   8.461%   $197.3556   $197.36   $197.35   $197.40  
  Purchase #6 $61.91   12.504%   $69.6512   $69.65   $69.65   $69.70  
  Purchase #7 $25.99   7.372%   $27.906   $27.91   $27.90   $27.90  
  7 purchase totals = $894.09       $966.3190   $966.33   $966.30   $966.40