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 $125.74   11.432%   $140.1146   $140.11   $140.10   $140.10  
  Purchase #2 $136.51   3.811%   $141.7124   $141.71   $141.70   $141.70  
  Purchase #3 $72.34   6.615%   $77.1253   $77.13   $77.15   $77.10  
  Purchase #4 $206.73   8.319%   $223.9279   $223.93   $223.95   $223.90  
  Purchase #5 $182.55   11.796%   $204.0836   $204.08   $204.10   $204.10  
  Purchase #6 $208.67   13.329%   $236.4836   $236.48   $236.50   $236.50  
  Purchase #7 $208.68   8.688%   $226.8101   $226.81   $226.80   $226.80  
  7 purchase totals = $1,141.22       $1,250.2575   $1,250.25   $1,250.30   $1,250.20