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 $193.70   5.558%   $204.4658   $204.47   $204.45   $204.50  
  Purchase #2 $181.99   11.255%   $202.473   $202.47   $202.45   $202.50  
  Purchase #3 $133.81   5.565%   $141.2565   $141.26   $141.25   $141.30  
  Purchase #4 $241.37   10.119%   $265.7942   $265.79   $265.80   $265.80  
  Purchase #5 $162.82   11.106%   $180.9028   $180.90   $180.90   $180.90  
  Purchase #6 $33.62   7.266%   $36.0628   $36.06   $36.05   $36.10  
  Purchase #7 $22.77   6.153%   $24.171   $24.17   $24.15   $24.20  
  7 purchase totals = $970.08       $1,055.1261   $1,055.12   $1,055.05   $1,055.30