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 $38.82   11.342%   $43.223   $43.22   $43.20   $43.20  
  Purchase #2 $147.59   4.844%   $154.7393   $154.74   $154.75   $154.70  
  Purchase #3 $180.32   11.565%   $201.174   $201.17   $201.15   $201.20  
  Purchase #4 $232.35   13.651%   $264.0681   $264.07   $264.05   $264.10  
  Purchase #5 $215.47   9.179%   $235.248   $235.25   $235.25   $235.20  
  Purchase #6 $156.99   10.596%   $173.6247   $173.62   $173.60   $173.60  
  Purchase #7 $57.69   11.776%   $64.4836   $64.48   $64.50   $64.50  
  7 purchase totals = $1,029.23       $1,136.5607   $1,136.55   $1,136.50   $1,136.50