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 $115.66   5.385%   $121.8883   $121.89   $121.90   $121.90  
  Purchase #2 $119.72   11.252%   $133.1909   $133.19   $133.20   $133.20  
  Purchase #3 $111.95   10.264%   $123.4405   $123.44   $123.45   $123.40  
  Purchase #4 $141.62   4.536%   $148.0439   $148.04   $148.05   $148.00  
  Purchase #5 $25.26   5.106%   $26.5498   $26.55   $26.55   $26.50  
  Purchase #6 $75.81   8.463%   $82.2258   $82.23   $82.25   $82.20  
  Purchase #7 $11.99   9.206%   $13.0938   $13.09   $13.10   $13.10  
  7 purchase totals = $602.01       $648.4330   $648.43   $648.50   $648.30