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 $13.56   7.629%   $14.5945   $14.59   $14.60   $14.60  
  Purchase #2 $176.58   5.388%   $186.0941   $186.09   $186.10   $186.10  
  Purchase #3 $246.36   7.684%   $265.2903   $265.29   $265.30   $265.30  
  Purchase #4 $50.98   11.731%   $56.9605   $56.96   $56.95   $57.00  
  Purchase #5 $175.97   5.140%   $185.0149   $185.01   $185.00   $185.00  
  Purchase #6 $151.44   7.484%   $162.7738   $162.77   $162.75   $162.80  
  Purchase #7 $236.47   10.838%   $262.0986   $262.10   $262.10   $262.10  
  7 purchase totals = $1,051.36       $1,132.8267   $1,132.81   $1,132.80   $1,132.90