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 $90.61   8.114%   $97.9621   $97.96   $97.95   $98.00  
  Purchase #2 $148.82   13.399%   $168.7604   $168.76   $168.75   $168.80  
  Purchase #3 $8.58   7.442%   $9.2185   $9.22   $9.20   $9.20  
  Purchase #4 $55.26   4.249%   $57.608   $57.61   $57.60   $57.60  
  Purchase #5 $144.46   12.563%   $162.6085   $162.61   $162.60   $162.60  
  Purchase #6 $159.58   12.481%   $179.4972   $179.50   $179.50   $179.50  
  Purchase #7 $178.99   11.802%   $200.1144   $200.11   $200.10   $200.10  
  7 purchase totals = $786.30       $875.7691   $875.77   $875.70   $875.80