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 $242.51   12.418%   $272.6249   $272.62   $272.60   $272.60  
  Purchase #2 $35.41   12.836%   $39.9552   $39.96   $39.95   $40.00  
  Purchase #3 $167.41   12.694%   $188.661   $188.66   $188.65   $188.70  
  Purchase #4 $202.46   10.800%   $224.3257   $224.33   $224.35   $224.30  
  Purchase #5 $61.63   12.671%   $69.4391   $69.44   $69.45   $69.40  
  Purchase #6 $203.70   10.351%   $224.785   $224.79   $224.80   $224.80  
  Purchase #7 $190.42   12.676%   $214.5576   $214.56   $214.55   $214.60  
  7 purchase totals = $1,103.54       $1,234.3485   $1,234.36   $1,234.35   $1,234.40