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 $185.42   11.397%   $206.5523   $206.55   $206.55   $206.60  
  Purchase #2 $42.38   3.263%   $43.7629   $43.76   $43.75   $43.80  
  Purchase #3 $170.85   5.784%   $180.732   $180.73   $180.75   $180.70  
  Purchase #4 $79.77   10.718%   $88.3197   $88.32   $88.30   $88.30  
  Purchase #5 $111.59   8.399%   $120.9624   $120.96   $120.95   $121.00  
  Purchase #6 $242.47   11.685%   $270.8026   $270.80   $270.80   $270.80  
  Purchase #7 $43.76   12.132%   $49.069   $49.07   $49.05   $49.10  
  7 purchase totals = $876.24       $960.2009   $960.19   $960.15   $960.30