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 $54.56   13.423%   $61.8836   $61.88   $61.90   $61.90  
  Purchase #2 $186.89   4.211%   $194.7599   $194.76   $194.75   $194.80  
  Purchase #3 $218.81   5.844%   $231.5973   $231.60   $231.60   $231.60  
  Purchase #4 $118.68   11.805%   $132.6902   $132.69   $132.70   $132.70  
  Purchase #5 $192.30   7.802%   $207.3032   $207.30   $207.30   $207.30  
  Purchase #6 $240.84   4.125%   $250.7747   $250.77   $250.75   $250.80  
  Purchase #7 $9.97   12.649%   $11.2311   $11.23   $11.25   $11.20  
  7 purchase totals = $1,022.05       $1,090.2400   $1,090.23   $1,090.25   $1,090.30