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 $32.59   8.548%   $35.3758   $35.38   $35.40   $35.40  
  Purchase #2 $115.60   3.699%   $119.876   $119.88   $119.90   $119.90  
  Purchase #3 $50.55   4.254%   $52.7004   $52.70   $52.70   $52.70  
  Purchase #4 $74.97   9.695%   $82.2383   $82.24   $82.25   $82.20  
  Purchase #5 $87.75   9.702%   $96.2635   $96.26   $96.25   $96.30  
  Purchase #6 $217.87   11.503%   $242.9316   $242.93   $242.95   $242.90  
  Purchase #7 $56.35   12.841%   $63.5859   $63.59   $63.60   $63.60  
  7 purchase totals = $635.68       $692.9715   $692.98   $693.05   $693.00