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 $58.97   6.290%   $62.6792   $62.68   $62.70   $62.70  
  Purchase #2 $116.61   8.238%   $126.2163   $126.22   $126.20   $126.20  
  Purchase #3 $109.91   4.766%   $115.1483   $115.15   $115.15   $115.10  
  Purchase #4 $168.91   7.175%   $181.0293   $181.03   $181.05   $181.00  
  Purchase #5 $11.76   12.720%   $13.2559   $13.26   $13.25   $13.30  
  Purchase #6 $61.71   5.538%   $65.1275   $65.13   $65.15   $65.10  
  Purchase #7 $103.65   8.766%   $112.736   $112.74   $112.75   $112.70  
  7 purchase totals = $631.52       $676.1925   $676.21   $676.25   $676.10