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 $233.77   8.131%   $252.7778   $252.78   $252.80   $252.80  
  Purchase #2 $240.51   11.524%   $268.2264   $268.23   $268.25   $268.20  
  Purchase #3 $241.97   3.394%   $250.1825   $250.18   $250.20   $250.20  
  Purchase #4 $198.62   8.145%   $214.7976   $214.80   $214.80   $214.80  
  Purchase #5 $40.58   13.138%   $45.9114   $45.91   $45.90   $45.90  
  Purchase #6 $48.82   11.281%   $54.3274   $54.33   $54.35   $54.30  
  Purchase #7 $237.38   12.474%   $266.9908   $266.99   $267.00   $267.00  
  7 purchase totals = $1,241.65       $1,353.2139   $1,353.22   $1,353.30   $1,353.20