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 $60.41   4.500%   $63.1285   $63.13   $63.15   $63.10  
  Purchase #2 $208.62   11.606%   $232.8324   $232.83   $232.85   $232.80  
  Purchase #3 $151.98   11.439%   $169.365   $169.37   $169.35   $169.40  
  Purchase #4 $49.36   11.424%   $54.9989   $55.00   $55.00   $55.00  
  Purchase #5 $113.69   12.602%   $128.0172   $128.02   $128.00   $128.00  
  Purchase #6 $41.76   5.736%   $44.1554   $44.16   $44.15   $44.20  
  Purchase #7 $174.82   9.859%   $192.0555   $192.06   $192.05   $192.10  
  7 purchase totals = $800.64       $884.5529   $884.57   $884.55   $884.60