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 $155.28   13.669%   $176.5052   $176.51   $176.50   $176.50  
  Purchase #2 $64.77   11.520%   $72.2315   $72.23   $72.25   $72.20  
  Purchase #3 $70.60   11.851%   $78.9668   $78.97   $78.95   $79.00  
  Purchase #4 $155.69   8.843%   $169.4577   $169.46   $169.45   $169.50  
  Purchase #5 $235.62   13.126%   $266.5475   $266.55   $266.55   $266.50  
  Purchase #6 $44.38   10.769%   $49.1593   $49.16   $49.15   $49.20  
  Purchase #7 $177.76   13.228%   $201.2741   $201.27   $201.25   $201.30  
  7 purchase totals = $904.10       $1,014.1421   $1,014.15   $1,014.10   $1,014.20