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 $85.79   13.122%   $97.0474   $97.05   $97.05   $97.00  
  Purchase #2 $173.40   10.825%   $192.1706   $192.17   $192.15   $192.20  
  Purchase #3 $183.44   8.424%   $198.893   $198.89   $198.90   $198.90  
  Purchase #4 $13.77   13.219%   $15.5903   $15.59   $15.60   $15.60  
  Purchase #5 $128.53   9.367%   $140.5694   $140.57   $140.55   $140.60  
  Purchase #6 $23.47   10.467%   $25.9266   $25.93   $25.95   $25.90  
  Purchase #7 $222.32   11.769%   $248.4848   $248.48   $248.50   $248.50  
  7 purchase totals = $830.72       $918.6821   $918.68   $918.70   $918.70