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 $183.26   13.683%   $208.3355   $208.34   $208.35   $208.30  
  Purchase #2 $54.69   10.424%   $60.3909   $60.39   $60.40   $60.40  
  Purchase #3 $84.92   5.160%   $89.3019   $89.30   $89.30   $89.30  
  Purchase #4 $203.70   11.239%   $226.5938   $226.59   $226.60   $226.60  
  Purchase #5 $113.38   9.685%   $124.3609   $124.36   $124.35   $124.40  
  Purchase #6 $34.63   7.252%   $37.1414   $37.14   $37.15   $37.10  
  Purchase #7 $183.94   7.233%   $197.2444   $197.24   $197.25   $197.20  
  7 purchase totals = $858.52       $943.3688   $943.36   $943.40   $943.30