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 $237.51   6.117%   $252.0385   $252.04   $252.05   $252.00  
  Purchase #2 $208.31   11.342%   $231.9365   $231.94   $231.95   $231.90  
  Purchase #3 $149.83   3.439%   $154.9827   $154.98   $155.00   $155.00  
  Purchase #4 $133.71   6.381%   $142.242   $142.24   $142.25   $142.20  
  Purchase #5 $199.67   13.216%   $226.0584   $226.06   $226.05   $226.10  
  Purchase #6 $179.65   3.469%   $185.8821   $185.88   $185.90   $185.90  
  Purchase #7 $169.59   8.639%   $184.2409   $184.24   $184.25   $184.20  
  7 purchase totals = $1,278.27       $1,377.3811   $1,377.38   $1,377.45   $1,377.30