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 $58.77   13.496%   $66.7016   $66.70   $66.70   $66.70  
  Purchase #2 $181.30   6.755%   $193.5468   $193.55   $193.55   $193.50  
  Purchase #3 $8.38   10.736%   $9.2797   $9.28   $9.30   $9.30  
  Purchase #4 $234.99   5.805%   $248.6312   $248.63   $248.65   $248.60  
  Purchase #5 $214.95   9.771%   $235.9528   $235.95   $235.95   $236.00  
  Purchase #6 $213.29   3.848%   $221.4974   $221.50   $221.50   $221.50  
  Purchase #7 $127.63   12.782%   $143.9437   $143.94   $143.95   $143.90  
  7 purchase totals = $1,039.31       $1,119.5532   $1,119.55   $1,119.60   $1,119.50