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 $43.94   8.511%   $47.6797   $47.68   $47.70   $47.70  
  Purchase #2 $174.95   11.180%   $194.5094   $194.51   $194.50   $194.50  
  Purchase #3 $242.36   11.871%   $271.1306   $271.13   $271.15   $271.10  
  Purchase #4 $198.84   13.702%   $226.0851   $226.09   $226.10   $226.10  
  Purchase #5 $44.44   6.119%   $47.1593   $47.16   $47.15   $47.20  
  Purchase #6 $50.56   10.138%   $55.6858   $55.69   $55.70   $55.70  
  Purchase #7 $165.60   8.291%   $179.3299   $179.33   $179.35   $179.30  
  7 purchase totals = $920.69       $1,021.5798   $1,021.59   $1,021.65   $1,021.60