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 $57.69   10.701%   $63.8634   $63.86   $63.85   $63.90  
  Purchase #2 $188.46   12.798%   $212.5791   $212.58   $212.60   $212.60  
  Purchase #3 $112.31   10.643%   $124.2632   $124.26   $124.25   $124.30  
  Purchase #4 $97.50   8.395%   $105.6851   $105.69   $105.70   $105.70  
  Purchase #5 $173.70   13.751%   $197.5855   $197.59   $197.60   $197.60  
  Purchase #6 $249.39   5.487%   $263.074   $263.07   $263.05   $263.10  
  Purchase #7 $55.56   3.428%   $57.4646   $57.46   $57.45   $57.50  
  7 purchase totals = $934.61       $1,024.5149   $1,024.51   $1,024.50   $1,024.70