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 $52.76   13.573%   $59.9211   $59.92   $59.90   $59.90  
  Purchase #2 $199.63   9.409%   $218.4132   $218.41   $218.40   $218.40  
  Purchase #3 $55.89   11.435%   $62.281   $62.28   $62.30   $62.30  
  Purchase #4 $201.26   6.616%   $214.5754   $214.58   $214.60   $214.60  
  Purchase #5 $21.96   6.119%   $23.3037   $23.30   $23.30   $23.30  
  Purchase #6 $59.48   7.232%   $63.7816   $63.78   $63.80   $63.80  
  Purchase #7 $250.67   8.705%   $272.4908   $272.49   $272.50   $272.50  
  7 purchase totals = $841.65       $914.7668   $914.76   $914.80   $914.80