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 $181.97   13.722%   $206.9399   $206.94   $206.95   $206.90  
  Purchase #2 $90.62   5.254%   $95.3812   $95.38   $95.40   $95.40  
  Purchase #3 $168.89   5.339%   $177.907   $177.91   $177.90   $177.90  
  Purchase #4 $108.97   5.258%   $114.6996   $114.70   $114.70   $114.70  
  Purchase #5 $206.58   11.672%   $230.692   $230.69   $230.70   $230.70  
  Purchase #6 $153.26   12.420%   $172.2949   $172.29   $172.30   $172.30  
  Purchase #7 $30.50   5.778%   $32.2623   $32.26   $32.25   $32.30  
  7 purchase totals = $940.79       $1,030.1769   $1,030.17   $1,030.20   $1,030.20