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 $17.60   4.737%   $18.4337   $18.43   $18.45   $18.40  
  Purchase #2 $118.92   12.359%   $133.6173   $133.62   $133.60   $133.60  
  Purchase #3 $157.59   10.765%   $174.5546   $174.55   $174.55   $174.60  
  Purchase #4 $42.92   3.678%   $44.4986   $44.50   $44.50   $44.50  
  Purchase #5 $229.77   8.129%   $248.448   $248.45   $248.45   $248.40  
  Purchase #6 $141.76   6.588%   $151.0991   $151.10   $151.10   $151.10  
  Purchase #7 $153.58   9.221%   $167.7416   $167.74   $167.75   $167.70  
  7 purchase totals = $862.14       $938.3929   $938.39   $938.40   $938.30