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 $147.58   13.559%   $167.5904   $167.59   $167.60   $167.60  
  Purchase #2 $181.56   10.287%   $200.2371   $200.24   $200.25   $200.20  
  Purchase #3 $33.76   3.524%   $34.9497   $34.95   $34.95   $34.90  
  Purchase #4 $239.62   6.800%   $255.9142   $255.91   $255.90   $255.90  
  Purchase #5 $155.49   4.149%   $161.9413   $161.94   $161.95   $161.90  
  Purchase #6 $159.86   5.435%   $168.5484   $168.55   $168.55   $168.50  
  Purchase #7 $155.61   9.291%   $170.0677   $170.07   $170.05   $170.10  
  7 purchase totals = $1,073.48       $1,159.2488   $1,159.25   $1,159.25   $1,159.10