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 $23.96   8.328%   $25.9554   $25.96   $25.95   $26.00  
  Purchase #2 $46.83   10.597%   $51.7926   $51.79   $51.80   $51.80  
  Purchase #3 $39.77   4.107%   $41.4034   $41.40   $41.40   $41.40  
  Purchase #4 $29.66   6.186%   $31.4948   $31.49   $31.50   $31.50  
  Purchase #5 $50.31   13.619%   $57.1617   $57.16   $57.15   $57.20  
  Purchase #6 $164.37   7.187%   $176.1833   $176.18   $176.20   $176.20  
  Purchase #7 $199.73   11.676%   $223.0505   $223.05   $223.05   $223.10  
  7 purchase totals = $554.63       $607.0417   $607.03   $607.05   $607.20