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 $63.26   13.270%   $71.6546   $71.65   $71.65   $71.70  
  Purchase #2 $203.69   4.620%   $213.1005   $213.10   $213.10   $213.10  
  Purchase #3 $127.58   5.756%   $134.9235   $134.92   $134.90   $134.90  
  Purchase #4 $49.68   13.552%   $56.4126   $56.41   $56.40   $56.40  
  Purchase #5 $127.37   5.791%   $134.746   $134.75   $134.75   $134.70  
  Purchase #6 $86.27   7.358%   $92.6177   $92.62   $92.60   $92.60  
  Purchase #7 $208.25   11.145%   $231.4595   $231.46   $231.45   $231.50  
  7 purchase totals = $866.10       $934.9144   $934.91   $934.85   $934.90