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 $167.95   8.771%   $182.6809   $182.68   $182.70   $182.70  
  Purchase #2 $80.94   4.660%   $84.7118   $84.71   $84.70   $84.70  
  Purchase #3 $163.65   7.717%   $176.2789   $176.28   $176.30   $176.30  
  Purchase #4 $241.81   5.833%   $255.9148   $255.91   $255.90   $255.90  
  Purchase #5 $69.75   10.197%   $76.8624   $76.86   $76.85   $76.90  
  Purchase #6 $59.95   3.787%   $62.2203   $62.22   $62.20   $62.20  
  Purchase #7 $203.26   12.222%   $228.1024   $228.10   $228.10   $228.10  
  7 purchase totals = $987.31       $1,066.7715   $1,066.76   $1,066.75   $1,066.80