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 $184.38   11.157%   $204.9513   $204.95   $204.95   $205.00  
  Purchase #2 $97.44   13.859%   $110.9442   $110.94   $110.95   $110.90  
  Purchase #3 $188.94   10.360%   $208.5142   $208.51   $208.50   $208.50  
  Purchase #4 $173.36   13.844%   $197.36   $197.36   $197.35   $197.40  
  Purchase #5 $135.88   8.366%   $147.2477   $147.25   $147.25   $147.20  
  Purchase #6 $63.41   9.303%   $69.309   $69.31   $69.30   $69.30  
  Purchase #7 $185.75   7.124%   $198.9828   $198.98   $199.00   $199.00  
  7 purchase totals = $1,029.16       $1,137.3092   $1,137.30   $1,137.30   $1,137.30