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 $84.38   12.852%   $95.2245   $95.22   $95.20   $95.20  
  Purchase #2 $11.31   6.200%   $12.0112   $12.01   $12.00   $12.00  
  Purchase #3 $105.92   8.120%   $114.5207   $114.52   $114.50   $114.50  
  Purchase #4 $198.56   13.855%   $226.0705   $226.07   $226.05   $226.10  
  Purchase #5 $110.27   3.223%   $113.824   $113.82   $113.80   $113.80  
  Purchase #6 $134.97   4.242%   $140.6954   $140.70   $140.70   $140.70  
  Purchase #7 $193.94   7.147%   $207.8009   $207.80   $207.80   $207.80  
  7 purchase totals = $839.35       $910.1472   $910.14   $910.05   $910.10