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 $24.91   6.566%   $26.5456   $26.55   $26.55   $26.50  
  Purchase #2 $143.91   10.590%   $159.1501   $159.15   $159.15   $159.20  
  Purchase #3 $69.25   11.564%   $77.2581   $77.26   $77.25   $77.30  
  Purchase #4 $161.36   12.200%   $181.0459   $181.05   $181.05   $181.00  
  Purchase #5 $198.36   3.705%   $205.7092   $205.71   $205.70   $205.70  
  Purchase #6 $241.35   9.312%   $263.8245   $263.82   $263.80   $263.80  
  Purchase #7 $164.47   6.211%   $174.6852   $174.69   $174.70   $174.70  
  7 purchase totals = $1,003.61       $1,088.2186   $1,088.23   $1,088.20   $1,088.20