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 $212.46   11.487%   $236.8653   $236.87   $236.85   $236.90  
  Purchase #2 $87.74   9.303%   $95.9025   $95.90   $95.90   $95.90  
  Purchase #3 $63.28   13.383%   $71.7488   $71.75   $71.75   $71.70  
  Purchase #4 $155.87   12.857%   $175.9102   $175.91   $175.90   $175.90  
  Purchase #5 $91.62   13.283%   $103.7899   $103.79   $103.80   $103.80  
  Purchase #6 $168.57   10.457%   $186.1974   $186.20   $186.20   $186.20  
  Purchase #7 $155.69   8.711%   $169.2522   $169.25   $169.25   $169.30  
  7 purchase totals = $935.23       $1,039.6663   $1,039.67   $1,039.65   $1,039.70