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 $120.29   13.527%   $136.5616   $136.56   $136.55   $136.60  
  Purchase #2 $24.68   10.403%   $27.2475   $27.25   $27.25   $27.20  
  Purchase #3 $22.63   10.766%   $25.0663   $25.07   $25.05   $25.10  
  Purchase #4 $52.88   5.466%   $55.7704   $55.77   $55.75   $55.80  
  Purchase #5 $44.26   9.677%   $48.543   $48.54   $48.55   $48.50  
  Purchase #6 $88.57   8.256%   $95.8823   $95.88   $95.90   $95.90  
  Purchase #7 $85.65   13.514%   $97.2247   $97.22   $97.20   $97.20  
  7 purchase totals = $438.96       $486.2958   $486.29   $486.25   $486.30