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 $122.93   9.509%   $134.6194   $134.62   $134.60   $134.60  
  Purchase #2 $176.85   10.795%   $195.941   $195.94   $195.95   $195.90  
  Purchase #3 $64.98   5.828%   $68.767   $68.77   $68.75   $68.80  
  Purchase #4 $113.79   12.248%   $127.727   $127.73   $127.75   $127.70  
  Purchase #5 $33.95   4.562%   $35.4988   $35.50   $35.50   $35.50  
  Purchase #6 $126.28   6.166%   $134.0664   $134.07   $134.05   $134.10  
  Purchase #7 $194.53   5.873%   $205.9547   $205.95   $205.95   $206.00  
  7 purchase totals = $833.31       $902.5743   $902.58   $902.55   $902.60