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 $64.88   5.856%   $68.6794   $68.68   $68.70   $68.70  
  Purchase #2 $179.81   12.732%   $202.7034   $202.70   $202.70   $202.70  
  Purchase #3 $132.42   8.608%   $143.8187   $143.82   $143.80   $143.80  
  Purchase #4 $5.55   3.736%   $5.7573   $5.76   $5.75   $5.80  
  Purchase #5 $12.97   8.523%   $14.0754   $14.08   $14.10   $14.10  
  Purchase #6 $182.75   7.667%   $196.7614   $196.76   $196.75   $196.80  
  Purchase #7 $52.89   12.732%   $59.624   $59.62   $59.60   $59.60  
  7 purchase totals = $631.27       $691.4196   $691.42   $691.40   $691.50