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 $58.80   11.665%   $65.659   $65.66   $65.65   $65.70  
  Purchase #2 $192.80   8.597%   $209.375   $209.38   $209.40   $209.40  
  Purchase #3 $81.53   4.123%   $84.8915   $84.89   $84.90   $84.90  
  Purchase #4 $232.58   9.129%   $253.8122   $253.81   $253.80   $253.80  
  Purchase #5 $133.59   5.710%   $141.218   $141.22   $141.20   $141.20  
  Purchase #6 $175.85   12.176%   $197.2615   $197.26   $197.25   $197.30  
  Purchase #7 $155.71   7.451%   $167.312   $167.31   $167.30   $167.30  
  7 purchase totals = $1,030.86       $1,119.5292   $1,119.53   $1,119.50   $1,119.60