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 $61.93   10.319%   $68.3206   $68.32   $68.30   $68.30  
  Purchase #2 $27.26   4.393%   $28.4575   $28.46   $28.45   $28.50  
  Purchase #3 $187.26   10.614%   $207.1358   $207.14   $207.15   $207.10  
  Purchase #4 $50.33   13.143%   $56.9449   $56.94   $56.95   $56.90  
  Purchase #5 $231.93   9.669%   $254.3553   $254.36   $254.35   $254.40  
  Purchase #6 $169.99   13.173%   $192.3828   $192.38   $192.40   $192.40  
  Purchase #7 $155.76   13.400%   $176.6318   $176.63   $176.65   $176.60  
  7 purchase totals = $884.46       $984.2287   $984.23   $984.25   $984.20