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 $81.45   6.643%   $86.8607   $86.86   $86.85   $86.90  
  Purchase #2 $223.34   13.592%   $253.6964   $253.70   $253.70   $253.70  
  Purchase #3 $46.62   5.184%   $49.0368   $49.04   $49.05   $49.00  
  Purchase #4 $171.62   7.319%   $184.1809   $184.18   $184.20   $184.20  
  Purchase #5 $63.59   7.725%   $68.5023   $68.50   $68.50   $68.50  
  Purchase #6 $106.85   7.767%   $115.149   $115.15   $115.15   $115.10  
  Purchase #7 $108.25   6.487%   $115.2722   $115.27   $115.25   $115.30  
  7 purchase totals = $801.72       $872.6983   $872.70   $872.70   $872.70