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 $192.52   11.671%   $214.989   $214.99   $215.00   $215.00  
  Purchase #2 $87.71   11.412%   $97.7195   $97.72   $97.70   $97.70  
  Purchase #3 $58.43   10.546%   $64.592   $64.59   $64.60   $64.60  
  Purchase #4 $226.64   5.794%   $239.7715   $239.77   $239.75   $239.80  
  Purchase #5 $110.44   3.742%   $114.5727   $114.57   $114.55   $114.60  
  Purchase #6 $226.82   11.772%   $253.5213   $253.52   $253.50   $253.50  
  Purchase #7 $166.25   4.294%   $173.3888   $173.39   $173.40   $173.40  
  7 purchase totals = $1,068.81       $1,158.5548   $1,158.55   $1,158.50   $1,158.60