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 $23.86   10.393%   $26.3398   $26.34   $26.35   $26.30  
  Purchase #2 $62.73   8.489%   $68.0551   $68.06   $68.05   $68.10  
  Purchase #3 $201.43   4.663%   $210.8227   $210.82   $210.80   $210.80  
  Purchase #4 $205.32   4.239%   $214.0235   $214.02   $214.00   $214.00  
  Purchase #5 $19.25   8.532%   $20.8924   $20.89   $20.90   $20.90  
  Purchase #6 $173.89   13.585%   $197.513   $197.51   $197.50   $197.50  
  Purchase #7 $197.76   12.274%   $222.0331   $222.03   $222.05   $222.00  
  7 purchase totals = $884.24       $959.6796   $959.67   $959.65   $959.60