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 $98.65   4.819%   $103.4039   $103.40   $103.40   $103.40  
  Purchase #2 $242.63   3.327%   $250.7023   $250.70   $250.70   $250.70  
  Purchase #3 $22.45   8.631%   $24.3877   $24.39   $24.40   $24.40  
  Purchase #4 $208.26   8.164%   $225.2623   $225.26   $225.25   $225.30  
  Purchase #5 $198.75   11.457%   $221.5208   $221.52   $221.50   $221.50  
  Purchase #6 $60.39   13.280%   $68.4098   $68.41   $68.40   $68.40  
  Purchase #7 $193.84   11.178%   $215.5074   $215.51   $215.50   $215.50  
  7 purchase totals = $1,024.97       $1,109.1942   $1,109.19   $1,109.15   $1,109.20