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 $40.73   9.564%   $44.6254   $44.63   $44.65   $44.60  
  Purchase #2 $175.38   10.568%   $193.9142   $193.91   $193.90   $193.90  
  Purchase #3 $240.67   5.798%   $254.624   $254.62   $254.60   $254.60  
  Purchase #4 $102.53   11.716%   $114.5424   $114.54   $114.55   $114.50  
  Purchase #5 $135.69   4.813%   $142.2208   $142.22   $142.20   $142.20  
  Purchase #6 $114.47   10.479%   $126.4653   $126.47   $126.45   $126.50  
  Purchase #7 $44.73   9.573%   $49.012   $49.01   $49.00   $49.00  
  7 purchase totals = $854.20       $925.4041   $925.40   $925.35   $925.30