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 $233.75   8.672%   $254.0208   $254.02   $254.00   $254.00  
  Purchase #2 $88.95   8.609%   $96.6077   $96.61   $96.60   $96.60  
  Purchase #3 $177.42   4.732%   $185.8155   $185.82   $185.80   $185.80  
  Purchase #4 $85.77   7.598%   $92.2868   $92.29   $92.30   $92.30  
  Purchase #5 $188.51   7.533%   $202.7105   $202.71   $202.70   $202.70  
  Purchase #6 $72.99   13.576%   $82.8991   $82.90   $82.90   $82.90  
  Purchase #7 $146.30   10.523%   $161.6951   $161.70   $161.70   $161.70  
  7 purchase totals = $993.69       $1,076.0355   $1,076.05   $1,076.00   $1,076.00